May 3 World number seven Juan Martin del Potro has withdrawn from next week's Madrid Open because of a viral infection, organisers said on Friday.
The heavy-hitting Argentine reached the semi-finals last year before losing to Czech Tomas Berdych.
"He has a virus and will not be fit to play," a statement on the tournament's website (www.madrid-open.com) said. "We wish him a fast recovery."
Belgian David Goffin, who was in the qualifying tournament, will take Del Potro's place in the main draw.
The claycourt Masters Series tournament features the big four of world number one Novak Djokovic, defending champion Roger Federer, Andy Murray and Rafael Nadal.
(Writing by Martyn Herman, editing by Ed Osmond)