Novak Djokovic accidentally struck Roger Federer with a forehand as the doubles team were beaten at the Laver Cup on Friday.
Djok and Fed united
The Serbian saw a forehand hit Federer, who was standing at the net, in the back during their clash against Kevin Anderson and Jack Sock.
Djokovic was stunned by his mishit, later rubbing Federer's back before the pair spoke about the incident at a change of ends.
"That's why we don't play doubles," Federer said to Djokovic.
Djokovic responded: "Oh my God, I think my heart stopped for like three seconds."
Incredibly, Federer and Djokovic – with 34 grand slam titles between them – suffered Team Europe's only loss in Chicago.
The pair went down to Anderson and Sock 6-7 (5-7) 6-3 10-6, but Europe led 3-1 at the end of the opening day after earlier singles wins by Grigor Dimitrov, Kyle Edmund and David Goffin.