Defending French Open champion Stan Wawrinka says Roger Federer's withdrawal from this year's tournament is "scary" and "sad for tennis".
Federer announced that he would sit out the tournament at Roland Garros having suffered with a back problem in recent weeks.
The world number three's absence brings an end to his remarkable run of 65 consecutive grand slam appearances, which started in 2000 and included a win in Paris in 2009.
"It makes me sad and it's scary. It's bizarre to say that he won't be in Paris," fellow Swiss Wawrinka is quoted as telling Switzerland's ATS news agency.
"It proves that we are never safe from injury.
"It's sad for tennis, a big blow for his fans and especially for him as he's had a very difficult season.
"His 65 consecutive Grand Slam appearances are the kind of statistics that allows everyone to see everything he has accomplished."
Federer will hope to recover in time to play at Wimbledon, which begins at the end of June.