Novak Djokovic said Sunday he needs "some time" to rediscover top form after his historic season was interrupted by a six-week injury break.
The top-ranked Serb resumes at the Swiss Indoors with a 64-3 record this year, after a back muscle injury forced him to retire from a Davis Cup semifinal singles match against Juan Martin del Potro of Argentina on September 18.
"Certainly, it's going to take me some time to get back to the right shape," Djokovic said.
The US Open, Wimbledon and Australian Open champion faces 50th-ranked Belgian Xavier Malisse on Tuesday in Basel, the hometown tournament of 16-time Grand Slam singles winner Roger Federer.
"I don't expect myself to be 100 percent in this tournament but obviously I will try," said Djokovic, who beat Federer in the 2009 final here and lost their rematch a year ago.
Djokovic succumbed to pain that had flared up days earlier during his intense, 4-set victory over Rafael Nadal to earn his first US Open trophy.
Though the muscle tear was "quite bad," Djokovic acknowledged the timing was a blessing.
"The injury is never welcome ... but it came in the right moment, let's say. It gave me a little more time to rest and recover," he said. "I think it was the longest (break) I had in the last four or five years."
Djokovic said he had daily therapy on his back while missing the Asian tournament swing, and a shot at beating John McEnroe's dominant 82-3 season record in 1984.
He now has just Basel, the Paris Masters and season-ending ATP World Tour Finals in London remaining, and must win all three to get close to the American's mark.
"I don't feel unbeatable and I don't think anybody is," Djokovic cautioned. "It's just a matter of the right momentum, the confidence you are building up.
"Sometimes you see the ball as a water melon. You feel so good on the court, you trust every shot that you have. I guess every top player has experienced that and has experienced the bad times as well."
The good times really rolled for Djokovic after leading Serbia to its first Davis Cup title last December in an emotional final in Belgrade against France.
His determination to help defend that title worsened the injury he brought home from New York.
"I decided to play Davis Cup which turned out to be a wrong decision somehow for my health," Djokovic said. "But I don't regret it because I do things as well with my heart and I wanted to play for the Davis Cup team."
The enforced break also took Djokovic out of the spotlight having become world number one on winning Wimbledon in July.
"I think I'm doing well handling everything that (comes) with the new position that I have. I haven't changed my professionalism or anything like that in the last couple of months," he said.
"We're trying to do things that we always have done and keep a simple life. That's the only way I can keep playing well and performing well and winning titles."
Djokovic believes that he "matured mentally" - on and off the court - to create a foundation for success.
"It took me maybe longer than I expected to really start believing that I can win Grand Slams next to Roger and Rafa," he said.
He has also talked of marrying his longtime girlfriend Jelena Ristic.
"Whoever says you have to make a line between private life and professional life, I don't think that's true," Djokovic said.
"It has to be balanced. You cannot run away from that fact. I got everything together in my private life as well."