Howe revealed on Dubravka: "He has not been feeling very well for a couple of days so hopefully he is on the mend."
Asked about Karius' selection, he added: "He has trained every day for a long period of time. He had a slight shoulder injury at the start of the season but since then he has been fine. He has played in games behind closed doors so he is match ready.
"The last game he played of course was the cup final so he is used to big games and at Liverpool he had many big matches so I have no doubt about his temperament and we are relying on his big-game experience."