The shot stopper found it difficult to recover from his Champions League final in 2018 against Real Madrid.
Scans at Massachusetts General Hospital in Boston after the game revealed that Karius had a concussion.
Speaking to SPORTBible, he said: "It has been difficult to shake off. Even at other clubs when I was trying to gain a manager's trust or get game time when I felt like, in my opinion, I deserved it…
"There have definitely been moments where I've thought that was my disadvantage.
"It might not even be the manager's fault but if you know you have a player that is going to draw so much attention then it's going to add pressure.
"They've probably thought, ‘I'll take the easy and safe way rather than go the other route.’
"You can understand in some ways but it's frustrating when there isn't much else you can do to change their mind."
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