Andy Murray says he "would be very surprised" if he can play at the French Open.
The world No 2 was forced to retire hurt during his ATP Rome Masters match with Marcel Granollers on Wednesday after suffering a recurrence of a lower back problem.
And a despondent Murray, who was supposed to be celebrating his 26th birthday in Rome, delivered a grim verdict on his chances of competing at Roland Garros later this month.
"I have an issue with my lower back," he said. "It's been an issue for a while.
"I would be very surprised if I was playing in Paris. I need to make a plan as to what I do. I'll chat with the guys and make a plan for the next few days then make a decision on Paris after the next five days.
"I want to make sure it goes away. It's been a problem since the end of 2011 but it got bad during last year's clay season."
Murray's match with Granollers was tied at 1-1 in sets when he quit, and his opponent was sympathetic.
Granollers said: "He is a good player and he can do well in Roland Garros, and if he has a problem then I can understand he is thinking of Paris."