Carvalhal was reacting to Leroy Fer's suspected Achilles injury.
"I can do some speculation, I don't know but at first view it looks serious," he said.
"We think it's his Achilles and not something light but let's see tomorrow or the next 48 hours, we'll analyse him.
"But I must say Carroll did very well. The level of Carroll improved the team, he gave energy and played very good on the ball, improved the dynamic. Part of what we achieved in the second half was with the participation of Carroll.
"Unlucky for Fer, but a lucky situation for Carroll, who came into the side and performed very well."
Meanwhile, Carvalhal has revealed Swansea have complained about his internet bill!
“Me and my staff do a lot of work – you don't realise how many hours we discuss the opponents," he said.
“I arrive at 8 o'clock. Sometimes I go home at 6 o'clock or half six, it depends, but sometimes my staff are still working. I don't know what time they leave because they are always working.
“When I leave to go home at 6 o'clock most of the time I go to analyse videos again.
“I was frustrated a little bit because the internet is very slow. The club must have spent a lot of money because I used the 4G.
“They said 'hey, you are using a lot of 4G!'
“I said 'yes, because the internet is slow and I have to work'. I used a lot of money and it wasn't good, but now the internet is okay, it has been fixed!"