Nalbandian was disqualified after falling behind in the second set of Sunday's AEGON Championships final. He won the first set 7-6 (7-3) but slipped behind Marin Cilic 3-4 in the second after dropping serve.
He reacted by kicking an advertising sign around the chair of line judge Andrew McDougall, who suffered a cut on his left shin.
Nalbandian, who apologized to McDougall, was disqualified at that point and Cilic was awarded the championship.
The default cost Nalbandian the second-place check of more than $57,000 and 150 ranking points. The ATP said the fine of $12,560 was the maximum allowed.
London police also said they are investigating the incident as an assault after a complaint was filed.
Nalbandian,from Argentina, said he didn't think the incident amounted to a default.
"Sometimes you get very frustrated on court and it's tough to control that and sometimes I do a mistake. So it's very tough to end a final like that," he said. "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."