Russia's Daniil Medvedev Photo: Kirsty Wigglesworth/AP

Russia's Daniil Medvedev stunned Wimbledon on Wednesday when he threw coins at the umpire's chair before apologising for the bizarre gesture which he insisted was not meant to imply the official was corrupt.

The 21-year-old, who had shocked world number three Stan Wawrinka in the first round, lost 6-4, 6-2, 3-6, 2-6, 6-3 to Belgian qualifier Ruben Bemelmans.

Medvedev had been 2-0 up in the decider before he lost his composure and asked for female umpire Mariana Alves to be replaced.

His request was refused and after shaking hands with the official at the end of the match, he reached into his bag, took out his wallet and threw two handfuls of coins at the umpire's chair.

"In the heat of the moment, I did a bad thing. I apologise for this," said world number 49 Medvedev who had also been docked a point by Alves as his 2-0 final set lead melted into a 5-2 deficit.

Medvedev insisted he could not remember what he had said to Alves.

"It was a long match and very hot. I was just frustrated, so it had no meaning. I apologise for this."

"It was really stupid but it was not like this (meant as an indication that he considered the official to have biased).

"I was ready to leave the court, but that's what happened. I don't even remember what the coins were."

Wednesday's meltdown on Court 16 was not the first time the fiery Russian has been in trouble at a tournament.

He was disqualified from the Charleston clay court event in 2016 for launching into a racist rant, accusing umpire Sandy French of favouring black player Donald Young.

French is also black.

Medvedev said that incident was a misunderstanding.

"What I can tell is that I'm not racist at all. That's the only thing I will tell. And about the situation, it was a misunderstanding," he explained after Monday's win against Wawrinka.

Bemelmans, who goes on to face Sam Querrey of the United States, said he had realised that his opponent was getting increasingly frustrated at a series of over-rules.

"There are some players who play better after chatting with the umpire. I said to myself no, keep do what you are doing, it's working, you lose nothing. He started to make mistakes so that broke his concentration, discussing with the umpire," said the Belgian.

On the coin-throwing incident, he added: "I haven't seen it. I don't even know what he did there.

"Obviously in the fifth set after that call on 30-40 at 2-1, he was not happy but I think it was the right call to make. If he wants to be pissed off, that's his problem. That's his decision. It happens in tennis and he should get over it."