Federer won the Madrid Masters in 2006 and was a finalist in 2007 in the event, which this year begins on Saturday with qualification matches and ends on October 19.

The Swiss had a layoff of two weeks as he skipped this week's Stockholm Open.

The tournament could pit Federer against Rafael Nadal for the first time since the Spaniard assumed the No. 1 ranking, which the Swiss star had held for a record 237 weeks.

Federer was knocked out of the Olympic tournament in Beijing before a potential matchup with Nadal, who won the gold medal.

The pair haven't met since Nadal ended Federer's bid for a sixth straight Wimbledon crown in June.