"It's great being with the boys again," tweeted Federer, above a Swiss team picture including himself and Wawrinka with arms around each other.
In the shot, world number four Wawrinka makes playful 'bunny ears' behind his team-mate's head.
That frivolity seemed light years from the fallout between the two countrymen as Federer defeated Wawrinka in three gruelling sets 4-6, 7-5, 7-6 (8/6) on Saturday evening in the ATP World Tour Finals semi-finals.
Federer had saved three match points in the tenth game of the deciding set in that match and it was poised at 5-5 and 40-40 in game 11 when Warwinka gestured to Federer's box asking that they not make noise in between serves.
Federer's wife Mirka was sitting in the players section and Federer was reportedly upset that Wawrinka had blamed her.
The two were then seen involved in a long and tense discussion in the locker-room after the match and on Monday each went their own way en route from London to Lille in northern France for the Davis Cup showdown.
As it turned out Federer was unable to play in Sunday's final in London as he was laid low with back spasms, casting doubts on his ability to play against the French and win the Davis Cup for the first time in his distinguished career.
Federer said on Tuesday he was "hopeful" of being able to represent Switzerland on Friday.
"I am not good enough to practice yet and I wish my progress would be faster," the 17-time Grand Slam winner told a press conference at the Stade Pierre Mauroy outside Lille, which will host the three-day Davis Cup final.
"It's a little bit better than on Saturday, Sunday, Monday so I am hopeful."
"The world number two said that the Swiss team's medical staff had been working hard on his fitness and that the pain he had felt on Saturday was easing.
Asked if he was worried about missing the chance to win the Davis Cup final for the first time in his career, he replied: "I don't know — I'm a positive kind of person so I have to believe in it."
Sunday's withdrawal was only the third walkover of Federer's career and he has never abandoned a game during play.
Widely regarded as being the finest tennis player of all time, Federer has won all there is to win at the top in tennis apart from Olympic singles gold and the Davis Cup.
His greatest rival Rafael Nadal on the other hand has the full set of all four Grand Slam titles, Olympic singles gold and the Davis Cup.
Federer has blown hot and cold on the Davis Cup over the course of his long career, but with Wawrinka, this year's Australian Open champion, finally emerging as a player of the highest-class, a Davis Cup win has been a priority for him.
The London dogfight between the Swiss, the intensity of which astonished many people in France, has cast a cloud over those hopes.
In stark contrast it has been all plain sailing for the French who are seeking a 10th Davis Cup title in all and a first since 2001.
Captain Arnaud Clement cloistered his team of Jo-Wilfried Tsonga, Gael Monfils, Richard Gasquet and reserve Gilles Simon, none of whom qualified for the London finals, in Bordeaux where they honed their claycourt skills away from prying eyes.
The French as hosts have chosen an indoor claycourt as the surface for the final believing that gives them a better chance of defeating the two higher-ranked Swiss players.
Doubles specialist Julien Benneteau, who was playing in the doubles in London, then linked up with them after they decamped to Lille.