Amorim does hope the problem will not keep the centre-back out of action for too long, with Wolverhampton Wanderers up next on Monday night.
A busy spell follows throughout the month as the festive calendar ramps up.
"It's hard because, if you see that position, especially this year, it's just Harry [Maguire] and Matta playing those positions," he told Premier League Productions.
"It is a blow. He is playing really really well. But I'm really excited with Ayden [Heaven]. He is working there. I think he has the right characteristics to play there.
"It is a big opportunity for everyone to see Ayden.