Personal opinion: You don't make 15 changes to your squad in one season, you get some in, see how they gel, then work on the next lot the following window. I think we need to get in another player before we sell McT, we do it with a targeted player in mind who is both better than McT and is
completely happy to play second fiddle to Casemiro and our other expected midfield signing. If we sell McT we should be buying in someone who will carry out that backup role and not moan, and will commit themselves to the club. This is why players like O'Shea, Fletcher and yes, McT, are great: They will play their heart out even if they don't play every game. They are content to be second XI, not on high wages, but will still do their best.
On a completely different note, there's also the Homegrown rules.
2021/22:
Jones
Maguire
Pogba (gone)
Rashford
Grant (gone)
Lingard (gone)
Heaton
Shaw
Henderson (gone)
Wan-Bissaka
McTominay
With Jones, Maguire, Rashford, Heaton, Shaw, Wan-Bissaka, McTominay - that's seven out of eight of our homegrown requirements. Now, Sancho I believe has graduated, so that would make our eight. None of our current four players we have bought are home-grown. Technically Kovar would no longer count as an U-21 player but I'm not sure we'll want to use him in our 25 man squad.
So, if we sell McT, we'll be one short on our 25 man squad due to home grown players. So we'll want to bring in someone who qualifies to replace him. So, I suppose the question is - can we find a player that:
1) is home grown talent
2) is happy to play backup to our new midfield players, likely behind Fred too
3) is happy to do this for low wages
4) is better than McTominay
5) is low cost enough to justify the expense for a 3rd/4th choice in their position
and I'm not so sure that would be such an easy find. I just don't think it's the right time to get rid of McT, personally. I'd absolutely get rid of the non-homegrown deadwood first. People seem to think we can have 25 first team players from outside our team, since they are also clamouring for the sales of Wan-Bissaka, Maguire, Jones, Rashford and in some cases people even think we should get rid of Shaw and Heaton (although that's not as regularly called for, thankfully). Seems we just hate homegrown players these days.
Shockingly, Greenwood still qualifies as an U-21 player so the club don't have to look
completely stupid for still paying his wages despite not even putting him into our 25 man squad.