I don't think he has anything to apologize for after all the coach is finding it hard to admit that he has done wrong. Sancho on the other hand, has only committed one offense which is not being in his best form, so why on earth would the coach say he's not doing well in training? The player said he's doing fine, if the coach don't like him is best to say Sancho isn't in his plan and let the player start packing his stuff to any available club.
I have this feeling that this issue is on the palm of the coach, and I don't see this as a sign of discipline at all, ETH doesn't like Sancho and it won't help the team.
I don't think Sancho would help the team as well, instead of allowing his pride make his form to reduce more why not apologise to the coach so as to start training with the first team, maybe the coach would give him a chance to prove himself and show to the fans that the coach was wrong, by displaying a very good performance on the pitch, after all Wambissaka was also called and even benched for Dalot but the coach but he worked hard to improve and impressed the coach.
That's almost the same thing with David de Gea, he never had that self pride, like saying something and stick to it no matter how dedicated he has been with the side, and Man UTD knew so they took advantage of the situation, that's why Manchester United player with him till they allowed him go. Now with Sancho, I think the player doesn't want same thing to happen to him and the coach shouldn't get away with it this time around. You can't just say something that's not true about me and get away with it and even expect me to apologize and make me look stupid, that's not cool.
Sometimes is better to forget as in never to buy what the managers tells the media because they can make the players look like the bad one and them the saint.
What I'm saying is that Sancho and Erik ten Hag should look for a way to settle it.
Erik Ten Hag is the coach of Manchester United and he knows what's best for his team, if they coach says you're not doing fine, or meeting up with his standards, then it's left for the player to be very punctual in the training ground and work hard to be at his best, instead of replying back to the coaches comment like Sancho did, a disrespect to the coach is like disrespecting the club, Sancho won't dare try such a thing if it were in Sir Alex Ferguson's era, i don't even think he would've made the 1st team.
You have said it all and I quite agree with you on this but you should never forget that sometimes these coaches over step their boundaries and they feel since they're the coach they're free to do whatever they feel like and they'd get away with it.
Players deserve their respect too.