It is no secret that Mainoo is hoping for a move away from United in the January transfer window, as his game time under manager Ruben Amorim continues to not be enough for the young midfielder.
The 20-year-old has played just 11 Premier League games under Amorim this season, all coming from off the bench.
Mainoo's "idiot" brother
Earlier this week, Mainoo’s brother Jordan did the midfielder no favours with a "FREE KOBBIE MAINOO" T-shirt, which he wore in the Old Trafford crowd.
Speaking on the Stick to Football podcast, Keane has torn into Jordan as he suggests he is not helping the situation.
"Are you telling me that he can't sit there for another six months? He might think the manager's on his way out in the summer. He's 20 years of age, what's wrong with sitting and learning your trade? And even if he's not getting a chance, we've all had to do it.
"Sometimes a manager is on your case and what you have to do is prove them wrong. Jamie made a point that he never felt like a regular at Liverpool, I never felt like that at United.
“Every day is your chance to prove yourself to the manager and when the manager is picking his team, (he goes) 'he has to play'. He's got to get that in his mindset.
"And when he's got his idiot of a brother doing all that... we shouldn't even be giving that kind of stuff the time of day. Sometimes you're just surrounded by idiots, especially the families."
The 20-year-old was keen to join Napoli in the summer, but United refused to sanction the move. Now, with the January transfer window just weeks away all eyes will be on Mainoo as he seeks to escape the club.