American player Frances Tiafoe has apologised for a furious outburst in which he repeatedly swore at the chair umpire following his defeat in the Shanghai Masters.

Tiafoe, 26, reacted angrily towards chair umpire Jimmy Pinoargote after losing 5-7 7-5 7-6 (7-5) to Russia's Roman Safiullin.

Tiafoe could face a fine of up to $60,000 (£46,000) with the tirade classified as a verbal abuse offence under ATP rules.

"I really apologise for the way I acted," the world number 17 wrote on Instagram.

"That is not who I am and not how I want to treat people."

Tiafoe's outburst came at the end of a match that turned on the American being given a time violation at 5-5 in the tie-break.

The two-time US Open semi-finalist claimed he tossed the ball up to serve, but Pinoargote disagreed it was a legitimate throw intended to start the point and penalised him.

Forced to start with a second serve, Tiafoe lost the point after an exciting all-court exchange for 6-5 to Safiullin, who clinched victory at the first attempt.

As Tiafoe walked towards the umpire's chair, he launched a flurry of expletives at Pinoargote in a prolonged outburst.

"I let my frustration in the heat of the moment get the best of me and I'm extremely disappointed with how I handled the situation," Tiafoe added.

"That's not acceptable behaviour and I want to apologise to the umpire, the tournament and the fans."

The incident may be escalated if tournament officials feel it was 'flagrant and particularly injurious to the success of a tournament, or singularly egregious'.

If Tiafoe's actions are considered an 'offence of aggravated behaviour' or 'conduct contrary to the integrity of the game', he could face a larger fine.