ATLANTA -- It wasn't the pain from falling and feeling his knee pop, although for an NBA player, that was like going through childbirth. Nor was it the MRI and the doctor's frown the next day that confirmed the obvious.

No, it was watching almost an entire season go by, and spending so many weeks in solitary accompanied only by a treadmill, and especially waiting to return to the floor here in training camp. That hurt the most for Lou Williams of the Atlanta Hawks and other players like him, of which there seems to be many these days.

"Being without basketball," he said, "is almost like being alone."

His ACL tear happened Jan. 18, which means the calendar year 2013 seems like it never started yet. After going through surgery and months of rehab, he's still working his way back, one pivot and one three-on-three workout at a time. If there's any consolation, he isn't alone. This upcoming NBA season has a sinister-sounding theme that's sure to make you wince: Year of the Comeback. Knee surgery is becoming the concussion of the NBA. About a dozen players, most of them All-Stars or close enough, will sport a scar or two, along with months of rust, when they hit the floor. And a basketball nation will collectively ask the chilling question: Will so-and-so ever be the same?

Williams has a quick answer for that, one that seems to be the mindset of many coming off surgery: "I think I'll pick up where I left off and I'll be better. I already know it."

Williams was in the midst of making an ordinary move for him when his leg buckled in the season's 39th game. He used Dr. James Andrews, orthopedic surgeon to the stars, for his procedure and spent several weeks rehabbing in Florida at Andrews' complex. It was a shock to the system for Williams, who'd never been hurt before, who'd just arrived in his hometown to play for the Hawks after turning pro straight from high school and spending seven decent seasons as a sixth man in Philly.

Williams is a scorer who specializes in pull-up mid-range jumpers when not using his quickness to reach the rim, and therefore his knees are crucial to his game. In that situation, players naturally wonder and sometimes worry about the end result: Will it all return after months of rehab?

Well, that depends.

ACL surgery was once a basketball career-killer or, in the case of Julius Erving, an injury that stole inches off your vertical. That's not the case, for the most part, these days. There are other more severe injuries, microfracture surgery being at the top, that are more restrictive. Amare Stoudemire was initially fine after microfracture and scored a big free agent contract from the Knicks, but has since required multiple surgeries to relieve pain and swelling and correct flaws. He still isn't the same and may never be.

Along with the age of the player and the style he plays, it's all about severity when it comes to these injuries. Some are more complicated than others and therefore require the most recovery and rehab time.

"It's a tough road," said Mike Brungardt. He spent 17 years as the Spurs strength coach and is now CEO of Pro Hoop Strength, a resource for basketball strength and conditioning which includes a number of NBA strength coaches as members. "Mentally it gets to be a grind because there's so many menial types of things they must do coming right out of the surgery, like getting range-of-motion back, breaking down scar tissue and improving their flexibility. Not only does it challenge them from a boredom standpoint, but it's physically painful trying to force the body back to where it was before."

The list of those working back from leg injuries seems heavier than usual. Besides Williams, there's Kobe Bryant, Danilo Gallinari, Russell Westbrook, Derrick Rose, Danny Granger, Andrew Bynum, Greg Oden, Rajon Rondo and Brandon Rush. Meanwhile, Ricky Rubio and Iman Shumpert eased back into action after the start of last season but were on a minutes diet. You could field a strong championship contender from that group alone.

The most glaring example is Rose, who took 17 months, almost twice the normal recovery period, to suit up. Rose also took plenty of heat, mainly for teasing Bulls fans last season and in the playoffs with his pre-game workouts, when in fact he was trying to recover more mentally than physically at that point.

"Every individual is different, every scenario is different, each injury is different," said Brungardt. "Derrick Rose is the face of the Bulls franchise and the last thing they want to do is put him back in action when he wasn't ready to go mentally. When it's a franchise player, teams tend to be more careful, whereas another player might be encouraged to come back quicker. That doesn't necessarily sound fair but that's the reality in most cases."

Among those watching Rose conduct those controversial one-on-one scrimmages was Williams and he, too wondered what was up.

"I was kind of curious to see what was taking him that long because I was dealing with the same injury," Williams said. "He was like a case study for me. I was watching everything that was being said and what he was doing. We were supposed to speak when he came to Atlanta but the crazy thing was, he was too busy working out and hitting the weight room. Look, he was the MVP when he got hurt. I don't think he was willing to come back and just be OK. I think he wanted to come back when he was sure he could be an MVP-caliber player. If he didn't feel that kind of confidence, he was going to keep rehabbing."

From the standpoint of importance to his team, Rose is perhaps No. 1 among the injured. Although the Bulls reached the second round without him, they need his scoring and presence to go further. Same for Westbrook; when he limped off the court in the playoffs, the Thunder followed him shortly thereafter.

The rest? Kobe, of course, although the Lakers aren't built for a title run even if he's the Kobe of 2005. That goes for Rondo in Boston. Granger is now the fourth option in Indiana, though that would've been the case without injury. Gallinari and Rubio have major roles but probably aren't difference-makers. Oden, Shumpert and Rush are role players. Bynum? Who knows.

With the Hawks, Williams will have a clear and defined and important purpose: Become an X-factor for the rebuilding Hawks. He turns only 28 in two weeks and is still in his prime.

"The city has really embraced me so much but I don't think I've really shown anything since I've been here," he said. "Atlanta doesn't know what I bring to the table yet. I feel there's a lot that I need to show, but there's a lot that I can show. I'm anxious to get started."

But not in a hurry, though. As with all of these injury cases, there's no timetable. A reasonable projection would have Williams back before the holidays, but he hasn't been cleared to practice yet and still needs to progress from three-on-threes to five-on-fives. For him, recovery is now nine months and counting.

"You've got to be careful and make the decisions for the long-term," he said. "I know that's painful for a lot of fans to hear."

Williams feels your pain. More than you know.