Second seed Novak Djokovic was handed a place in the French Open semi-finals on Monday when scheduled last eight opponent Fabio Fognini was forced out with a torn left thigh muscle.
The 24-year-old Italian, who had been due to play his first career Grand Slam quarter-final, suffered the injury in his marathon five-set fourth-round win over Albert Montanes on Sunday.
"It's the most difficult decision I've made. It was my first Grand Slam quarter-final and I am playing the best tennis of my career. However, this was the best decision," said Fognini, the first Italian man to reach the last eight in Paris since Renzo Furlan in 1995.
"I was crying last night. I had the treatment and I decided to retire. I had another scan this morning and we knew that to play would aggravate the injury to the left thigh. It was too risky. But this is sport, this is tennis."
Djokovic will have to wait to discover his semi-final opponent.
Gael Monfils and David Ferrer have yet to complete their last-16 match, which was suspended on Sunday evening, with the winner to face Roger Federer in the quarter-finals.
The eventual winner of that tie will face the Serb world number two on Friday for a place in the final.
Djokovic said he felt sympathy for Fognini, a player he has defeated in both of their career meetings.
"Walkover from Fognini. Bad luck for him, hope he recovers fast. Today I get to enjoy Paris in a different way," wrote the Serb on Twitter.
Fognini, the world number 49, beat Montanes 4-6, 6-4, 3-6, 6-3, 11-9 in a four hour 22 minute marathon on Sunday.
He saved five match points and needed a medical time-out for his left thigh injury, which left him virtually unable to move.
Djokovic, who reached the last eight with a 6-4, 6-4, 6-2 victory over Richard Gasquet to stretch his undefeated run to 43 matches overall and 41 since the start of the year, said Fognini's win had been sensational.
"It was one of the strangest wins I have ever seen in my life, really. It was incredible for him to come up with the win," said the Serb.
However, a walkover is not counted as a victory, so Djokovic will have to wait until the semi-final to try and equal John McEnroe's 1984 mark of a 42-match winning start to the season.