By Ian Chadband
LONDON (Reuters) - Switzerland's potential Davis Cup fairytale this weekend has become clouded by uncertainty over the fitness of Roger Federer and suggestions of strained relations between the all-time great and his team mate Stanislas Wawrinka.
The country is on tenterhooks to learn whether its favorite son Federer, struggling with a back injury, can recover from injury in time to cap his matchless individual career by joining Wawrinka and winning a first team 'World Cup' for his nation against France in Lille.
Everything had been going swimmingly in Federer's historic quest until Saturday evening's semi-final of the ATP World Tour finals, in which he ousted his equally in-form pal Wawrinka in an epic three-setter.
Yet not only did the draining final moments of Federer's win reawaken his old back trouble, forcing him to withdraw before Sunday's final against Novak Djokovic, but the late tension of the match also caused Wawrinka to offer sharp, unimpressed words toward his opponent's support team at courtside.
John McEnroe, the former American firebrand now commentating for ESPN, only threw more fuel on the flames with his revelations that the two players were engaged in a long post-match debate.
"Something went on in the locker-room, there was a long talk between the players that extended well into the night," said McEnroe.
"And the stress of that -- I can't confirm all of this -- but a lot of this went on and I don't think that helped the situation."
Near the end of an increasingly stressful match which was only settled by a final set tiebreak during which Federer picked up his injury, it had appeared Wawrinka was unhappy with the exuberance of the celebrations of Federer's camp, led by his wife Mirka and father Robbie.
One French TV station reported that it had picked up Wawrinka complaining: "She did the same thing at Wimbledon." The team mates had played there in a quarter-final in the summer.
Wawrinka, though, later downplayed the incident, saying that "nothing much, nothing special".
"Tense match, never easy," he said.
The pair were due to travel to France on Monday to start preparations for the final with Federer still hopeful of shaking off the injury, even though any recurrence of the back problems which hampered him so much in 2013 must be a long-term worry for the 33-year-old.
"The way I feel right now, there's no way I can compete at any level really," Federer said on Sunday. "Probably in a few days it's going to be better.
"This back spasm or whatever it might be, it's just not a fun thing to have during the day. It's just uncomfortable. But I'm positive and I'm hopeful that it's going to go away very soon."
(Editing by Ed Osmond)