"Joey is a good player. It is a big blow that Tomkins is out now. It is a good thing that we have Joey back. We are well covered," Bilic told reporters.
O'Brien returned to competitive action for the first time since July in the 0-0 draw against Liverpool in the first game at Anfield on Jan. 30.
Liverpool have injury problems of their own, although striker Daniel Sturridge was on the bench in the 2-2 draw with Sunderland on Saturday.
"We are well prepared for whatever team they come with," Bilic said.
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"If it is not Sturridge, it will be (Christian) Benteke. They have a lot of good strikers and the difference is the midfield."
Bilic is expecting Liverpool manager Juergen Klopp, who missed the Sunderland game due to an appendicitis, to return to the dugout.
"He (Klopp) will be back because he is like that. He is the leader. He likes to work. For him this is natural and he wants to be back," the Croatian said.
(Reporting by Simon Jennings in Bengaluru, editing by Ed Osmond)
