The move has taken place before the transfer window in Turkey closes on Friday and follows the Cameroon international not playing in United’s opening three Premier League games.

“We would like to wish Andre good luck,” said United in announcing the deal, which is subject to international clearance and registration.

Onana’s only appearance for Ruben Amorim’s side this season came in their shock Carabao Cup exit at the hands of League Two Grimsby.

The 29-year-old was signed from Inter Milan for £47.2m in July 2023 by former Old Trafford boss Erik ten Hag to replace David de Gea as United’s number one.

He has made 102 appearances for the club and was part of their 2024 FA Cup-winning side.

But his United spell has been punctuated by a number of mistakes and Belgian goalkeeper Senne Lammens, 23, was signed on deadline day from Royal Antwerp in a deal worth an initial 21m euros (£18.1m) plus add-ons.

Amorim, whose side visit Manchester City in the Premier League on Sunday, now has Lammens, Altay Bayindir and Tom Heaton as his goalkeeping options.

The move has yet to be finalised, but sources close to the player anticipate it being done in time for him to make his debut against Fenerbahce on Sunday, 14 September.

Turkey’s transfer window is open until Friday, leaving time to get a deal completed for Onana, who is on international duty with Cameroon.

Onana had been linked with another Turkish club, Galatasaray, but they opted to sign Ugurcan Cakir.

Cakir, who started Turkey’s World Cup qualifying win over Georgia on Thursday, joined from Trabzonspor on 2 September in a deal that could eventually be worth 36m euros (£31.2m).

Trabzonspor have been assessing alternatives since that deal was completed, and club sources believe Onana could have a major impact.

Letting Onana or Altay Bayindir leave United has been on the cards since the club signed Senne Lammens from Royal Antwerp on deadline day.

Although Old Trafford officials stressed the club were willing to have a senior squad including four goalkeepers, that was at odds with head coach Ruben Amorim’s stated desire to have a smaller squad in the absence of European football.

Tom Heaton is the fourth senior goalkeeper in the United ranks.

Onana had, in theory, ended last season as United’s number one goalkeeper given he started the Europa League final defeat by Tottenham.

However, after injuring his hamstring at the start of pre-season training, he missed all United’s warm-up games and was overlooked for their opening three Premier League matches, when Bayindir was chosen.

Onana did start the shock second-round EFL Cup defeat by League Two Grimsby last month, when he was at fault for the Mariners’ second goal.

The 29-year-old was signed from Inter Milan for £47.2m in 2023, with then United boss Erik ten Hag keen to be reunited with a goalkeeper he first worked with at Ajax.

Onana has rarely looked comfortable, though, and the decision to bring him in to replace four-time club player of the year David de Gea has repeatedly been questioned.

A succession of mistakes led to Onana being dropped for the Premier League defeat at Newcastle on 13 April, although he was recalled for the chaotic 5-4 Europa League quarter-final win over Lyon immediately afterwards.

The former Chelsea, Manchester United and Tottenham manager sprinted on to the pitch and attempted a knee slide as Sofyan Amrabat’s late goal in stoppage time earned a 3-2 victory on Sunday.

However, Mourinho was unhappy with home team Trabzonspor being awarded two penalties – both after video assistant referee (VAR) consultations – and thought his side should have had a spot-kick before Amrabat’s late winner.

The 61-year-old even questioned why he had come to Turkey.

Speaking at length to broadcaster beIN Sports, Mourinho criticised the performance of referee Oguzhan Cakir and VAR official Atilla Karaoglan.

“I blame the Fenerbahce people that brought me here,” said Mourinho, who took over at the club in June. “They told me only half of the truth.

“They didn’t tell me the whole truth because if they told me the whole truth, I wouldn’t come.

“But, with half of the truth and my boys, we fight opponents and the system.”

Mourinho added: “He [Karaoglan] was alert to give the two penalty decisions which the referee didn’t give and then he was having Turkish tea when it was a clear penalty for us and he didn’t give it.”

Fenerbahce moved to second in the Turkish top flight, five points behind leaders Galatasaray, after their win.

“The man of the match was Atilla Karaoglan,” added Mourinho.

“We didn’t see him but he was the referee. The referee was just a little boy that was there on the pitch, but the referee was Atilla Karaoglan.

“He goes from the invisible man to the most important man in the match.

“I think I am speaking on behalf of every Fenerbahce fan – we don’t want him again.

“We don’t want him as a VAR. We don’t want him on the pitch but, on the VAR, even less.”

Fenerbahce won 3-2 at Papara Park, Trabzon and their players were met with violence as they celebrated the victory.

Bright Osayi-Samuel and Michy Batshuayi both tried to intervene as security services entered the field.

“Above all, sport is gentlemanship,” Turkey’s Interior Minister Ali Yerlikaya posted on X.

“It is never acceptable for violence to take place on football pitches.

“An investigation has been initiated immediately to identify the spectators who entered the pitch and to investigate the incidents that took place at the end of the match”

Tensions started to rise in the 87th minute when objects were thrown on to the field after Batshuayi scored what proved to be the winner for visiting side Fenerbahce.

The Turkish Football Federation (TFF) called the events “unacceptable” and said in a statement that “the necessary criminal sanctions will be imposed on those responsible for these incidents”.

It is the latest in a series of other controversial incidents in the Turkish league during the 2023-24 season.

In December, referee Halil Umut Meler was struck by MKE Ankaragucu president Faruk Koca, leading to a suspension in Super Lig fixtures.

Fenerbahce sit second in the Super Lig, two points behind leaders Galatasaray, and are 30 points clear of Trabzonspor in third.