Tennis fans saddened by detail in Roger Federer photo at Laver Cup

Roger Federer has sent the tennis world into a frenzy after posting a selfie with his teammates at the Laver Cup, but fans couldn't help but notice that Rafa Nadal was missing.

Federer will bid an emotional farewell to professional tennis at the Laver Cup this weekend, revealing on Tuesday that he will only play doubles on Friday before making way for a replacement player.

'VERY HARD': Roger Federer's devastating admission about wife

'WHO KNOWS': Roger Federer's shock call on post-tennis career move

The Swiss legend is teaming up with Nadal, Novak Djokovic and Andy Murray on Team Europe - the first time all four members of the 'Big 4' have played on the same side.

Casper Ruud, Stefanos Tsitsipas, Cameron Norrie and Matteo Berrettini make up the rest of Team Europe's star-studded roster, with everyone posing for a selfie at a pre-tournament event on Wednesday.

However the only member of the team who wasn't present was Nadal, who will only arrive in London on Thursday before play begins on Friday.

The Spanish superstar has been spending some much-needed time with pregnant wife Xisca, while also attending a ceremony at the University of Alcala on Tuesday to receive the 'Camino Real Award' from King Felipe VI.

Fans were initially concerned about Nadal's absence from Laver Cup festivities so close to the event kicking off, before he eased those fears with a tweet on Wednesday.

"Hey… I am coming tomorrow… Landing in London in the morning… wait for me," the 22-time grand slam champion wrote.

Nevertheless, fans were saddened that Nadal missed out on the rare photo opportunity with his long-time rivals.

Roger Federer hoping to team up with Rafa Nadal

Speaking at a packed press conference earlier on Wednesday, Federer said he was hoping to play with Nadal in his doubles swansong on Friday.

Under Laver Cup rules, every player must feature in at least one singles match unless they are replaced before the second day.

Federer said he was hoping to play doubles on Friday before Berrettini replaces him in singles for the weekend.

"It's an event I don't want to mess with, but I know my limitations," Federer said, admitting his surgically-repaired knee wasn't up to playing singles competitively.

"I asked (Europe captain) Bjorn (Borg) if I could play one doubles, on Friday night, then Matteo comes in. I'm nervous, I haven't played in so long."

The Swiss legend added: "It is clear that the most beautiful thing would be to play doubles here with Nadal, because it has been my great rivalry."

The former World No.1 had earlier revealed how troubles with his knee forced his decision to retire before he wanted to, admitting he had "stopped believing".

Federer, whose most recent competitive match was a loss to Hubert Hurkacz in last year's Wimbledon quarter-finals, has been struggling with his right knee after a third surgery last year.

The 41-year-old Swiss told BBC Breakfast: "The last three years have been tough to say the least.

"I knew I was on very thin ice for the last year, ever since I played Wimbledon.

"I tried to come back but there was a limit to what I could do. And I stopped believing in it, to be honest."

Federer said after a scan a few months ago, "very quickly we realised this was it."

"Then the question becomes: how do you announce and when do you announce? This is when it becomes reality. It was OK but stressful," he added.

Federer said he is "totally happy to step away" from playing professionally having "totally overachieved in my mind" during his illustrious career.

with AAP

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.