The Nigeria defender was given extra time off following the Confederations Cup.
However, with defenders Adam Matthews, Charlie Mulgrew and Virgil van Dijk injured, plus Steven Mouyokolo signed but not available until the second leg next week, manager Neil Lennon has called upon the services of Ambrose earlier than expected.
"Efe Ambrose is in contention," said the Northern Irishman, who has also seen Victor Wanyama leave for Southampton.
"He looks great, he looks in good condition. These guys play almost 12 months a year. He has had a couple of weeks off.
"He had a heavy schedule with the Confederations Cup, had a holiday, did a little bit of training in Nigeria and then joined us and he looks fine.
"It probably would have been ideal for him to do a little bit of conditioning work but looking at him he looks in fine fettle."