Federer's return from knee surgery delayed by stomach virus

Roger Federer, of Switzerland, responds to a question during a news conference at the Miami Open tennis tournament, Thursday, March 24, 2016, in Key Biscayne, Fla. This is Federer's first tournament since recovering from knee surgery. (AP Photo/Lynne Sladky) (The Associated Press)

Roger Federer, of Switzerland, responds to a question during a news conference at the Miami Open tennis tournament, Thursday, March 24, 2016, in Key Biscayne, Fla. This is Federer's first tournament since recovering from knee surgery. (AP Photo/Lynne Sladky) (The Associated Press)

Angelique Kerber, of Germany, returns to Barbora Strycova during a match at the Miami Open tennis tournament in Key Biscayne, Fla., Friday, March 25, 2016. (AP Photo/Alan Diaz) (The Associated Press)

Roger Federer's return from knee surgery has been delayed by a stomach virus.

Federer was scheduled to play Friday for the first time in nearly two months at the Miami Open, but he withdrew shortly before the match because of the illness, which he has been battling for several days.

Federer has been sidelined since undergoing arthroscopic surgery Feb. 3 to repair torn cartilage in his left knee. The 2005-06 Key Biscayne champion hasn't played in the tournament since 2014.

Federer was replaced in the draw by lucky loser Horacio Zeballos, who faced Juan Martin del Potro in the second round.