Hoops boss Neil Lennon insists the match in Lisbon will be an even tougher proposition than their famous win over Barcelona in their last Champions League outing.
"This game will be the toughest of our group, they will be very motivated to beat us," he told BBC Scotland.
"We're going to come up against a very motivated team at home, who are very impressive at home and who are going very well domestically.
"If we can get through midweek with a draw or a win that would be marvellous."
"No-one would have expected us to beat Barcelona, it was a fantastic night, but it's gone, it's history," added the manager.
"I said to the guys, I'll take you out in 20 years for a pint and we'll talk about it, but it's gone now and we want to qualify and that's our whole focus.
"I want to qualify now, it would mean so much to the club.
"In the last 16 you just never know where it will take you."