Argentina's David Nalbandian (right) accidentally injures a line judge after kicking a hoarding during the Queen's Club final against Marin Cilic of Croatia.

British police are investigating a complaint of assault against Argentine player David Nalbandian after he injured a linesman in a petulant outburst during the final of the Queen's Club tournament in London at the weekend.

Nalbandian was leading Sunday's match 7-6, 3-3 when he dropped serve in the seventh game and reacted by kicking out at a wooden advertising board which disintegrated on impact and slammed into official Andrew McDougall's left leg. A shocked McDougall cried out and instantly clutched his shin. When he rolled up his trouser leg, blood could be seen seeping from the wound. He received some on-court attention before being escorted off the ground to the club's medical centre.

After prolonged discussions between officials, umpire Fergus Murphy disqualified Nalbandian for "unsportsmanlike behavior" and awarded the match to his Croatian opponent Marin Cilic.

"An allegation of assault has been made to us relating to an incident at the... tennis tournament and we are now investigating," a Scotland Yard spokesman said yesterday.

Nalbandian apologized after the incident, saying: "I know (what) I did (is) a mistake, 100 percent. I feel very sorry for the guy. I didn't want to do that. But sometimes you get angry and you cannot control those moments."

He now faces a fine of up to US$10,000 despite already forfeiting his prize money (at least US$56,800) and ranking points for the week.

He is still scheduled to play at Wimbledon, which starts next week.

Nalbandian insisted he shouldn't have been disqualified.

"But sometimes we feel so much pressure from the ATP to play a lot of tournaments. They don't do anything (for) us, and today I do a mistake and I have to pay like that. I agree I do a mistake but sometimes everybody do a mistake and I didn't feel it had to end like that, especially in a final."

ATP rules state that any violent action will result in an automatic default.

"It's an unfortunate situation for everyone involved, the spectators, the tournament, the sponsors, the players and the linesman," Brad Drewett, ATP executive chairman and president, said in a statement. "David certainly did not mean for this to happen, however the rules are very clear in a situation like this and causing injury to someone is an automatic default for any player."