Casemiro looked finished as a player last term, but the Brazilian has showcased his world-class qualities - particularly under Michael Carrick - with 11 goal involvements in the Premier League.
A screen in front of the United defence, as well as a difference maker in the final third, the 34-year-old has become irreplaceable.
But having already confirmed that he will depart at the end of the campaign, the Red Devils must find a way to replace him, and there are several possibilities.
Premier League players Elliot Anderson, Adam Wharton, Carlos Baleba and Sandro Tonali have all been linked, while Atalanta's Ederson is someone they've scouted abroad.
According to Sky reporter Sacha Tavolieri, United are "closely monitoring" his situation, but as it stands, the most "concrete interest" is from the Serie A.
Encouragingly for United, though, Ederson's "dream" move is the Premier League, and meetings have already taken place in recent weeks between the Brazilian's representatives and United.
Ederson - who has made 40 appearances in all competitions this term - sees his contract expire in June 2027, with a cut-price deal potentially on the cards for United.