He told The Independent: "Broony (Brown) is our leader, our captain, and it's a big blow for us, but I think we have the strength and the quality in our squad to replace him.
"Kris is the same as Broony. He is a key player for us, he creates a lot for the strikers. But we have the quality in the squad to replace anyone in the team, even though it's a big blow for us.
"Both of the games against Ajax, home and away, are very important for us and Ajax. It's a really crucial moment for us. They are important games, but we don't feel any extra pressure. We are at home and we will try to play our own way and try to win."
Neil Lennon's men are still searching for their first points in the Champions League this season after suffering successive defeats to AC Milan and Barcelona.