Roger Federer and Stanislas Wawrinka's falling out at the ATP World Tour Finals which threatens to damage Switzerland's Davis Cup hopes came after Mirka Federer labelled the Swiss No 2 a "cry baby", new video footage has revealed.

Wawrinka complained to umpire Cedric Mourier as his opponent's wife, whose court-side position was next to the Australian Open champion's position on the baseline as he prepared to receive serve in the 11<sup>th game of the deciding third set, barracked the Swiss No.2.

After hearing "cry baby" come from a female voice in the crowd, the 29-year-old Wawrinka is seen gesticulating towards Federer's box, which also included coach Stefan Edburg, and saying: "Not just before the serve, not just before the serve."

The confrontation led to late-night clear-the-air talks between Federer and Wawrinka at the end of the match, which saw the former prevail after nearly three hours having saved four match points.

Federer withdrew from the subsequent final against Novak Djokovic on Sunday due to a back injury, which is said to have been accentuated by the discussions, which leaves a question mark over his participation in this week's Davis Cup final against France.

Both Federer and Wawrinka travelled separately to Lille ahead of the tie but were pictured together as the Swiss team assembled on Monday along with captain Severin Luthi and fellow teammates Marco Chiudinelli and Michael Lammer.

After winning 17 grand slam titles, Olympic doubles gold and spending a record 237 consecutive weeks as world No.1, the Davis Cup remains the only major success missing from Federer's CV and with him turning 34 next August time is running out to achieve the feat.

Switzerland's Davis Cup team are set to face the press on Tuesday for the first time ahead of the tie, which begins on Friday with two singles rubbers which, fitness permitting, will likely see Federer and Wawrinka both in action.

Relations between the two players, which has always been regarded as respectful with both at the summit of the men's game, will be the primary subject put to Federer and Wawrinka with new evidence regarding the reason for their falling out likely to put further strain on the duo.