Italian Fabio Fognini apologised after being heard to say: "I wish a bomb would explode on this club" during his Wimbledon defeat by Tennys Sandgren.
Fognini was already under threat of a ban from two major tournaments for using misogynistic language to a female umpire at the US Open in 2017.
He lost 4-6 6-7 (12-14) 3-6 to American Sandgren in the third round.
"Something happened on court. If somebody feels offended, I say sorry. No problem," said the 32-year-old.
"Most of the time when you're on court, you're frustrated. For sure I was not happy about my performance today because I was knowing I have a lot to win in this case, because I think I have a good chance to win."
Fognini was fined a then record $27,500 (£21,600) at Wimbledon in 2014 for a series of offences during a first-round match.
After the US Open in 2017, he was given a suspended ban of two grand slam tournaments covering two years as well as a fine of more than £70,000, half of which was suspended.
Wimbledon must now decide how severely to punish Fognini for this latest act.
The world number 10 also took a medical time-out for treatment to a bloodied hand after punching his racket to the court in frustration.
Sandgren is through to the fourth round at Wimbledon for the first time and will face fellow American Sam Querrey on Monday.
Wimbledon was hit by a bomb during World World II that damaged the Centre Court roof.