Ten Hag is counting on both left-backs this term.
"Tyrell is now in a good place," Ten Hag told the press. "But he is not here because I only took players who could play games or be available for team training.
"He is not that far, but he is now in a progress situation. At a relatively short notice, he can again return into team training and then into team performance in games.
"I think it would be possible in two months."
On Amass, 17, he also said: "We have to make progress but we all see here a potential where we have seen in previous year.
"For instance, two years ago, (Alejandro) Garnacho last season. We had it during last season with Kobbie (Mainoo), but he is not that far now at this moment.
"Yet, if we train him well, if we coach him well, then, in three months, it's possible that he can be on that point. But, in this moment, he needs to catch up and he has to develop some skills already to play for Manchester United, competing for the highest positions in the league.
"But, with big talent, it can go up very quickly and that is very interesting to see if he is capable of doing this."