The Belgian stopper spent 10 weeks out after being caught in the face by Emile Heskey during the 2-2 draw against Aston Villa at the Stadium of Light in October.
"I knew I had to fight for my place because there is a lot of competition here, and I felt I was a bit unlucky to pick up the injury," Mignolet told safc.com.
"I had never been injured before so it was something new for me and I think I learned from it.
"It was strange having 10 weeks being only in the gym and not being able to train like I was used to.
"But I learned and was then lucky to come straight back into the team under the new gaffer."