Roger Federer's return to action from knee surgery has been delayed after he withdrew from the Miami Open with a stomach virus.
The seventeen-time Grand Slam champion, who has been out since the end of January due to a knee problem, was scheduled to play Juan Martin del Potro in the second round, but has been forced to pull out.
Rather than Del Potro automatically advancing into the next round, he will have to play the game as Federer did not compete in the first round.
Tournament organisers have confirmed that Horacio Zeballos will take the former world number one's place.
