Roger Federer is to take part in the Madrid Masters Series, which starts on Saturday, tournament organisers announced on Thursday.
They welcomed his decision, describing him as one of the main contenders for the title.
Federer won in Madrid in 2006 and was runner-up last year.
In August the Swiss tennis player lost his number one ranking to Spanish rival Raphael Nadal after 237 weeks. He has won only one grand slam title this year, in the US Open last month.
The Madrid tournament could pit the two together for the first time since Federer lost his Wimbledon crown to the Spaniard in July.
Federer has taken a break from the courts over the last three weeks, saying he wanted to try to recover his top form by the end of the year. Last week he withdrew from the Stockholm Open.
The Masters Series in Madrid ends on October 19.