Ten Hag said: "Obviously it's a knock.
"And of course, it's also... he didn't start at all. So it's his first start. He did well. He was very bright, very confident.
"I thought also there was a reason that, in the end, he was out of fitness and came off. We have to see tomorrow what it is."
It was Amad's first start for United in three years.
"I think Amad deserved it (his start) and there is a still a lot of competition in that position," added Ten Hag.
"So he was injured for a long time and he has built himself back. He deserved it and across the season with (Alejandro) Garnacho, with Antony, we have options and (Marcus) Rashford has also played there as well.
"But today I thought he deserved it and he played very good, he did what we expected him to do, he was brave, he was creative, defended very good and I was impressed with his performance."