The giant midfielder, 35, sharply divided opinion amongst supporters whilst at United from 2013-2019 – before departing for China.
But in a sign of the Red Devils’ poor start to the season, many fans want his unique attributes back.
The former Everton and Belgium star announced on social media he will end an “amazing journey” with his Chinese Super League club next summer.
He wrote: “At the end of this season, after five years, I will say goodbye to the great club of Shandong Taishan FC.
“I have had the privilege of wearing the legendary jersey of this club in 130 games and of contributing to an incredible string of successes: the Super League in 2021 and the CFA Cup in 2020, 2021 and 2022.
“These moments will always be in my memory.”
Fellaini pledged to “give everything” in a bid to win more honours in his final campaign.
And many Old Trafford supporters reckon the 6ft 4ins aerial monster would toughen up United’s spine.
“Come back to Man U,” urged one, and “Get a game for United I miss you,” posted another.
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Old Trafford boss Erik ten Hag spent £60million on Chelsea’s England midfielder Mason Mount, but the summer recruit is already injured after a poor start.
And Ten Hag also astonished many supporters by re-signing back central defender Jonny Evans on a one-year deal following his release from Leicester.
Fans quickly homed in on Mount’s disappointing start and Evans being the same age as Fellaini.
When one wrote, “Bring back Fellaini for rotation” another replied: “Wouldn’t put it past them we’ve brought Johnny Evans back so why not.”
And a third even claimed of the big Fella: “He is better than Mount.”