Feliciano Lopez of Spain quit because of a side muscle injury on Monday after losing the first five games of his first-round French Open match against Florent Serra of France.
The 15th-seeded Lopez pulled the muscle while practicing at Roland Garros on Thursday.
"In the beginning, I felt it was nothing really serious, but (the) day after, I couldn't play almost," Lopez said. "I tried to rest during the weekend just to try to play today, but it was impossible."
He said he hopes to be healthy in time for Wimbledon, which starts June 25.