Earlier this week, Amorim ruled Leny Yoro out until April while Harry Maguire is also a doubt for the clash with his former club. Ayden Heaven played well as the left centre-back against La Real on his first senior start and United also have Victor Lindelof to call upon.
Manuel Ugarte was, like Lindelof, an unused substitute at Old Trafford and Amorim could utilise the pair - as well as the likes of Toby Collyer and Christian Eriksen - as he aims to keep things fresh in the East Midlands.
"With the different competitions, we have to rotate," he added. "We are risking some players. For example, Casemiro, he was so tired.
"We didn't want to risk Ugarte. Because today was a decision: in one competition, Ugarte wanted to stay here. We have Mason Mount who will return really slow, Kobbie [Mainoo] will maybe return in a few weeks, I don't know for sure.
"Harry Maguire, who we tried not to risk, we will see for Sunday. We need all the players and I think against Lyon [in the Europa League quarter-finals] it will be a different kind of game. The physicality is going to be a different game, more demanding in that aspect and we have a lot of difficult games in the Premier League."