The 30-year-old was heard using insulting language to Swedish official Louise Engzell during his first-round defeat by fellow countryman Stefano Travaglia in New York City.

He was fined $24,000 (£19,000/€20,000) for three offences of unsportsmanlike conduct.

This will be deducted from his $50,000 (£39,000/€42,000) prize money for losing in the first round of the singles event.

Fognini issued an apology for his behaviour in a post on Twitter, saying: "First of all I would apologise to you fans, to the referee for what happened.

"It was just a very bad day, but it did not forgive my behaviour in the match.

"Although I'm a hot-head (and though I've been right in most circumstances) I was wrong.

"But in the end it's only a tennis game."

World number one Rafael Nadal has criticised US Open organisers for waiting three days before suspending Fognini, who played twice in the men’s doubles before the Grand Slam Board defaulted him today.

"Three days for that? I don't think so," the Spaniard was quoted as saying by BBC Sport.

"He has been out winning two matches since then.

"It is not the ideal situation.

"It would be much better to do it immediately, not three days later."

In a statement, US Open organisers said Fognini was provisionally suspended "pending a final determination whether a major offence has been committed" under the Grand Slam Code of Conduct.

It confirmed that US’s Nicholas Monroe and Australia’s John-Patrick Smith, who lost to Fognini and compatriot Simone Bolelli in the third round of the men's doubles, would take their place in the quarter-finals.

If Fognini is found to have committed a major offence, he could be fined up to $250,000 (£193,000/€211,000) and/or suspended from future Grand Slams.

In 2014, the Italian was given the biggest penalty in Wimbledon history when he was fined $27,500 (£21,000/€23,000) for unsportsmanlike conduct.

Action continued today at Flushing Meadows with five-time champion Roger Federer claiming a straight-sets win over Spain’s Feliciano Lopez to reach the fourth round. 

The third-seeded Swiss, who had been forced to five sets in his opening two matches, beat Lopez 6-3, 6-3, 7-5 at Flushing Meadows.

Awaiting him in the last-16 is Germany’s Philipp Kohlschreiber, who defeated Australia’s John Millman 7-5, 6-2, 6-4.

"I'm really excited how I feel after two five-setters," the 19-time Grand Slam champion was quoted as saying by BBC Sport.

"It was clearly nice to go up two sets to love for a change.

"Feels different from there."

Nadal, who is bidding for his third US Open title, had earlier recovered from a set down against Argentina’s Leonardo Mayer to win 6-7, 6-3, 6-1, 6-4.

He goes onto meet unseeded Ukrainian Alexandr Dolgopolov in the fourth round.

Dolgopolov, who is under investigation for suspicious betting activity in a match he played at the recent Winston-Salem Open in North Carolina, defeated Serbia's Viktor Troicki 6-1, 6-0, 6-4.

Argentina’s Juan Martín del Potro, the 24th seed, cruised into the last-16 with a 6-3, 6-3, 6-4 victory over 11th seed Roberto Bautista Agut of Spain.

Del Potro, who won the US Open in 2009, will next go up against sixth seed Dominic Thiem after the Austrian overcame France’s Adrian Mannarino 7-5, 6-3, 6-4.

Ninth seed David Goffin of Belgium booked his place in the fourth round after France’s Gael Monfils was forced to retire with an injury when trailing 5-7, 1-5.

Goffin will face Russia’s Andrey Rublev after he beat Bosnia and Herzegovina’s Damir Dzumhur 6-4, 6-4, 5-7, 6-4.

In the women’s singles draw, world number one Karolína Plíšková of Czech Republic saved a second-set match point before going on to defeat China’s Zhang Shuai 3-6, 7-5, 6-4 for a place in the fourth round.

Plíšková received treatment for an arm injury at the end of the second set, but played it down after her victory.

"I feel much better," she said.

"I did some recovery and just saw the physios and some ice bath and those stuff.

"Hopefully it will be fine.

"It just felt a little bit tight during the match."

Plíšková will do battle with Jennifer Brady in the last-16 after the American beat Romania’s Monica Niculescu 6-3, 4-6, 7-6.

French Open champion Jelena Ostapenko of Latvia fell to a shock 6-3, 6-2 defeat at the hands of Russia's Daria Kasatkina, the world number 38.

Kaia Kanepi will go onto meet Kasatkina after the Estonian prevailed 6-3, 2-6, 7-5 over Japan's Naomi Osaka.

Elsewhere in the women's draw, Lucie Šafářová of Czech Republic beat Japan's Kurumi Nara 6-3, 6-2.

She will next face the United States' CoCo Vandeweghe, who defeated 10th seed Agnieszka Radwańska of Poland 7-5, 4-6, 6-4.

Fourth seed Elina Svitolina of Ukraine overcame the US’s Shelby Rogers 6-4, 7-5 and will go onto meet another American Madison Keys, who battled back from a set down to beat Russia’s Elena Vesnina 2-6, 6-4, 6-1.