Federer, who is preparing for the Miami Open, was in Chicago on Monday to promote the tournament he founded – the Laver Cup.
The Swiss legend was joined by fellow ATP star Nick Kyrgios to launch the second edition of the competition which will be played from September 21 to September 23.
The 36-year-old, was part of the inaugural Laver Cup last year which saw Team Europe come out on top against a Rest of the World side in Prague.
Federer and Nadal paired up for the doubles and they beat Sam Query and Jack Sock.
And the world No 1 has explained why it meant so much to have the likes of Nadal rooting for him during his singles tie.
“It was amazing to team up with players who are normally your biggest rivals and have the chance to play on the same side of the net and be members of the same team,” Federer said.
“I play against guys like Rafael (Nadal), Marin (Cilic), Sasha (Zverev), Dominic (Thiem) and Tomas (Berdych) all the time, so to have them on my side, cheering me on, giving me advice and me doing the same for them, meant so much.”
Federer holds a 290-point advantage over Nadal in the ATP Tour rankings.
After seeing his 17-match winning streak come to an end against Juan Martin del Potro on Sunday in the Indian Wells final, he will be desperate to get back on the winning trail.
Federer, who has been given a bye for the first round of the Miami Open, is expected to begin his campaign on Saturday.