The manager told reporters: "Costa and Arda are important players but they're just names. It will either be them playing or two other players that we know.
"We'll examine Costa but we have other injury doubts too. They trained better yesterday but we'll wait and see.
"I don't feel as overwhelmed as some people think but I feel the weight of responsibility on my shoulders."
Costa, who has scored 36 goals in all competitions this season, was able to train with the team today.