The France international turned down a switch to the Saudi Pro League with Al-Nassr last summer in order to join Villa, who forked out £46.3m to prise him away from Bayer Leverkusen.
Diaby's debut campaign at Villa Park saw him score 10 goals and set up nine more in 54 matches as the Lions qualified for the Champions League, and his contract runs for another four seasons.
However, the 25-year-old is now on the verge of a swift exit, as the Birmingham Mail reports that he has flown to the Middle East to complete a £50.5m move to Al-Ittihad.
Diaby is set to undergo his medical in the coming hours before his switch to the former Saudi Pro League champions, who also employ N'Golo Kante, Fabinho and Karim Benzema.
The attacker will follow the likes of Douglas Luiz, Omari Kellyman and Tim Ireogbunam out of the Aston Villa exit door, but as one Frenchman departs, another may arrive.
Aston Villa 'exploring' move for Ligue 1 defender
Villa could use some of the monies raised from Diaby's sale to reinforce their backline, and Unai Emery is thought to have identified Rennes right-back Lorenz Assignon as a potential target.
The 24-year-old has already experienced a taste of Premier League football with Burnley, making 15 top-flight appearances in the second half of the 2023-24 season while on loan at Turf Moor.
Assignon scored one goal and set up two more for the Clarets, but his efforts were ultimately futile in the fight against the drop as Burnley went straight back down to the Championship.
Assignon is now back at Rennes, where his contract runs until 2027, but according to French outlet Foot Mercato, both he and the club's management team are keen to part ways this summer.
Aston Villa have supposedly been alerted to Assignon's availability, and the Lions may only need to fork out €10m (£8.4m) to bring him back to the Premier League for good.
Italian powerhouses Roma are also keeping a close eye on developments surrounding the right-back, who has three goals and six assists to show from 64 matches in a Rennes shirt.
Oli McBurnie 'closing in' on La Liga move
Back to players leaving England, and former Sheffield United striker Oli McBurnie is supposedly set to try out a new adventure in Spanish football.
The 28-year-old became a free agent when his contract with the Blades expired at the end of June, ending a five-year stint at Bramall Lane since his arrival from Swansea City.
Sheffield United shelled out £16.1m to sign McBurnie in 2019, but according to Fabrizio Romano, the Blades will now witness the Scotland international head to Las Palmas for free.
McBurnie is said to have verbally agreed a switch to the La Liga side, and he will undergo his medical on Friday before being officially announced as their latest recruit.
The striker managed 29 goals of his own in addition to seven assists in 159 matches for Sheffield United, including six goals and three assists from 21 Premier League games last term.
McBurnie's switch to Las Palmas will represent the 28-year-old's first taste of foreign action, having previously turned out for Barnsley, Bradford City, Newport County, Bristol Rovers and Chester FC.
Southampton 'plotting approach' for Championship attacker as Che Adams replacement
Speaking of strikers on the move, West Bromwich Albion's Brandon Thomas-Asante could reportedly replace Che Adams at Premier League new boys Southampton.
The Saints could not come to an agreement over a new contract with Scotland international Adams, who has now embarked on a new adventure in Serie A with Torino.
According to Football Insider, Russell Martin's side have identified Thomas-Asante as an ideal successor, with the West Brom attacker now in the final year of his Hawthorns contract.
The Ghana international managed a respectable 11 goals and two assists in 41 Championship appearances during the 2023-24 season, but West Brom are willing to sell him due to his contract situation.
Thomas-Asante was playing League Two football with Salford City just two seasons ago, joining the Baggies in a £290,000 deal in the summer of 2022, and West Brom can expect a healthy profit on the 25-year-old.