Martinez, who joined the Red Devils from Ajax in 2022, has made over 100 appearances for the club with several injures impacting his career in Manchester.
The Argentina international has been involved in major controversy in recent weeks after calling out United's hierarchy, including director of football Jason Wilcox, following their UEFA Champions League defeat to Atletico Madrid.
He later apologised, and started Sunday's 1-1 Premier League draw against Leeds United, but it appears his time at the club may over.
His present deal runs until June 2027, where United will release him as a free agent, but they are also open to January offers in the region of £50M.
Harry Maguire and Luke Shaw could also move on upon the expiry of their own contracts, as the club plan a defensive rebuild in 2027, amid ongoing links to Jarrad Branthwaite, Lewis Hall and Adrien Truffert.