London police are investigating an allegation of assault on a line judge after tennis star David Nalbandian flew into an on-court rage that caused an inch-long gash on a line judge's shin.

Nalbandian was one set up but down in the second set in his match against Marin Cilic at the AEGON Championships at London's Queen's Court on Sunday.

In front of a posh crowd at one of Europe's oldest tennis clubs, the Argentine ace snapped and kicked in an advertisement, which flew into a line judge Andrew McDougall's shin, causing him to bleed in front of the shocked fans.

"We are aware of an incident at the AEGON Championships on June 17," a Scotland Yard representative told the U.K.'s Daily Telegraph. "A complaint has been made and the Metropolitan Police Service is now investigating. The allegation is of assault."

After the embarrassing incident Nalbandian lost the match after being disqualified for unsportsmanlike conduct, and lost his nearly $56,000 in prize money. He may also be fined $10,000.

"I am sorry and remorseful for what happen in today's Queen's final. I had [no] intention of hitting the linesman and it was an unfortunate reaction to the loss of a point. I had the opportunity to apologize in person," Nalbandian said at a press conference following the match.

"I realize this was a very regrettable incident. Finally I apologize to the public, the director of the tournament and my fans and followers in Argentina and around the world," he added.

The incident, which comes a week before the start of The Championships at Wimbledon, was quite the embarrassment for Nalbandian, who is ranked number 30 in the world.

"It's certainly not going to do any wonders for his public image," BBC Sport's Andy Swiss said. "He's an experienced player, he's been around the block. And I have no doubt he'll come back from this."

Cilic, who won by default was bewildered after the incident. He said that he was sorry too.

"I'm really sorry for the guys it had to end like this," he said.

Incidentally, Queen's Club is the same venue where John McEnroe got into trouble for swearing at the chairman's wife over a mix up with a practice court booking.