Roger Federer will probably be watching his back if he ever takes the court again with Novak Djokovic in doubles.
Or he might just take his own advice to the Serb and stick to playing singles after his partner drilled him in the backside with an errant forehand on Friday’s opening day of the Laver Cup.
Djokovic’s mortified reaction was captured by courtside cameras in Chicago and he quickly rushed over to Federer to gently rub the offending spot.
Federer, 37, playfully shrugged off the incident, but had some words of advice for his partner at the next changeover.
"That’s why we don’t play doubles, bro!” he said of their first-ever doubles partnership, to the amusement of the crowd - scroll down to see the videos of the initial incident and subsequent conversation.
A still shaken Djokovic replied, “Oh my God, I think my heart stopped for like three times.”
The proximity and use of the on-court microphones are just one of the benefits of the Laver Cup, giving fans a rare glimpse into the conversations between players in between points and games.
The Team Europe pair were able to regather themselves after the shot of misfortune to win the first set in a tiebreak against Team World’s Kevin Anderson and Jack Sock but the Americans proved to be too tough for the duo, eventually coming out on top 6-7 (5), 6-3, 10-6.
Nevertheless, Team Europe lead 3-1 at the end of the opening day, with the remaining matches to be played on Saturday and Sunday.
Federer will be back in action on Saturday as he is due to face Nick Kyrgios in the second match on court in Chicago.
Elsewhere, Alex Zverev will play John Isner, Djokovic faces Anderson and David Goffin and Grigor Dimitrov will team up to play Sock and Kyrgios.