Andy Murray would not put a number on it but, as he left Rome last night, despondent and frustrated on a 26th birthday he would rather forget, the chances of him showing up in Paris for the French Open later this month seemed no more than 50-50.
The Scot was forced to retire during his second-round match at the Rome Masters yesterday with a recurrence of the back injury that affected him at Roland Garros last year and promptly said: "I would be very surprised if I play in Paris."
Reading into Murray's words is far from an exact science but the key to his decision-making over the next few days will be whether it affects his chances of glory at Wimbledon.
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Having gone so close 12 months ago when he was beaten in the final by Roger Federer, the world No.2 believes this year could be his best chance of becoming the first home men's champion since Fred Perry in 1936.
With one grand slam under his belt after last year's US Open victory, he is keen to add more major trophies to the cabinet and if there is any doubt whatsoever, as he suggested last night, then he will not be in Paris.
"The French Open is 10 days away now and you need to be practising and training 100% before going into a grand slam," he said. "The French is incredibly physical as well. The injury has come at a tough time so I need to make a decision and not do anything silly. The thing is, the whole year I try to peak for the slams and get in the best shape possible for them.
"Depending on what happens at the French I will obviously do everything I can to make sure I'm 100% for the next slam, which is Wimbledon, but we'll have to wait and see. "
That wait-and-see period will cover the next few days as Murray has treatment in London for what specifically, he said, is a disc problem in his lower back, on the left-hand side.
Against Granollers, he was wincing in pain at times, especially when stretching far to his left-hand side. He did well to recover from 4-1 down to win the second set but he said he quit because he did not think he would have been able to play the next match.
Twelve months ago, Murray had eight pain-killing injections in his back just before the French Open after back pain flared up and he then suffered from back spasms during the tournament itself, only to go on to reach the quarter-finals.
Murray said he has had the problem, on and off, since the end of 2011 and said the idea of having more pain-killing injections again was not appealing.
"You have the injections and obviously they can help a bit with pain and they can take some of the inflammation away," Murray said. "But that also didn't make me feel 100% and I want to feel 100%."
Having reached the final at Wimbledon, won the Olympics and then the US Open for his first grand slam title, Murray has a stack of points to defend in the second half of the year.
He will remain world No.2 at least until the end of the French Open despite his early defeat here but he knows he has to get his back problems in order in the long run if he is to maintain his quest for the top ranking.
"I will try to get it sorted in the coming weeks," he said. "Like I say, it's been an issue for a while now. I want to make sure it goes away and doesn't become something that I'm playing for a long, long time with."
Yesterday's withdrawal was only his second during competition, coming, coincidentally, six years to the day after he injured his wrist in Hamburg, an injury which kept him out for three months.
Clay, with the necessity to create your own pace at times and cope with high-bouncing balls, has proved troublesome for Murray and he admitted that grass should be easier for him to cope with. "There's not one thing that makes it feel much better and some days are better than others," he said. "But the quicker courts help and the lower bounces with a bit more pace off the surface also helps."
Rafael Nadal, chasing a seventh Rome title, made a convincing start with a 6-1, 6-3 win over Italy's Fabio Fognini but Stanislas Wawrinka, beaten finalist in Madrid last week, did not even make the court, the 15th seed pulling out with a thigh injury before his match against Alexandr Dolgopolov, who next meets Novak Djokovic. Jo-Wilfried Tsonga, the eighth seed, lost 6-4, 7-6 (7-5) to the exuberant Pole Jerzy Janowicz, who ripped open his shirt in celebration.