Basel, Switzerland: Roger Federer thinks he made mistakes this year by playing when injured, but insists he is ready for a strong finish to his most difficult season.
Ahead of his hometown Swiss Indoors tournament, Federer said he regretted playing matches with back problems at Indian Wells in March, and Hamburg and Gstaad in July.
"With hindsight, I shouldn't have done. They were errors," said the now seventh-ranked Federer, who has been one of the most durable players on tour throughout his career.
The 32-year-old Swiss said he felt "physically and mentally" prepared for a possible 15 matches in three season-ending weeks at Basel, the Paris Masters and ATP World Tour Finals in London.
Still, Federer — who has a relatively modest 36-13 season record — was cautious when asked if he could repeat his title hat trick of 2011.
"I don't know if my level of play is strong enough to do it now," he said. "That would be a bit bizarre for me if I start saying that I'm going to win the last 15 matches of the season.
"I have to hope so because I know that I can play really well, especially indoor. That starts here in Basel with the advantage of playing at home."
Federer, a five-time Swiss Indoors champion, opens Monday against 60th-ranked Frenchman Adrian Mannarino.
In his far from typical season, Federer has regularly lost to unseeded opponents since injuring his back in March.
Initially, he had shrugged off "a little tweak" after getting hurt during a routine victory over Ivan Dodig of Croatia in the BNP Paribas Open at Indian Wells, California.
"I should never have played after Dodig," Federer reflected on Sunday, saying he lost practice time in the following weeks.
After his shocking second-round defeat at Wimbledon, against Sergiy Stakhovsky of Ukraine, Federer opted to play on clay in July rather than rest to prepare for hard-court events ahead of the U.S. Open.
"I should have abandoned in Hamburg, not played Gstaad. Nevertheless, I played, I tried," said Federer, who sustained back-to-back losses against unheralded opponents.
As a result, Federer has yet to secure his place at the eight-man ATP finals which he has won a record six times.
Federer is fighting for one of the three remaining places with fellow Swiss Stanislas Wawrinka, and Frenchmen Jo-Wilfried Tsonga and Richard Gasquet, who won the Kremlin Cup title Sunday in Moscow.
Federer and Wawrinka could meet in the final at Basel, where they are seeded No. 3 and 4, respectively. Gasquet is the No. 5 seed.
"I will be happy if Stan qualifies," Federer said. "If that meant I will miss it, I honestly won't care. That means he was the better player for the year."