Canadian Vasek Pospisil has apologised for his on-court rant aimed at ATP Tour chief Andrea Gaudenzi in Miami yesterday where he was given a verbal abuse penalty by the chair umpire during his first-round loss to American Mackenzie McDonald.

Pospisil hit a ball out of the court shouting at the chair umpire, after smashing his racket late in the first set of his 6-3 4-6 6-3 defeat.

The verbal abuse penalty cost him the first set, but Pospisil then launched into an expletive-laden tirade against Gaudenzi.

The Canadian claimed Gaudenzi had screamed at him during a player meeting on Tuesday for “trying to unite the players”.

“For an hour and a half. The leader of the ATP. Get him out here. Why am I supporting this?” he said to chair umpire Arnaud Gabas, threatening to sue the ATP if he was defaulted.

Pospisil and world No.1 Novak Djokovic broke away from the ATP last year to form the Professional Tennis Players Association.

Pospisil later said his meeting with the ATP had “unnerved” him.

“I want to sincerely apologise for my behaviour on the court in Miami earlier today,” Pospisil said.

“By way of explanation, I felt deeply unnerved during a meeting between players and ATP executives last night, and I underestimated the toll those emotions took on me until I stepped onto the court today.

“Again, I am sorry for my on-court behaviour and the language I used.”