Neil Lennon says Celtic's Group H clash with Ajax on Tuesday is pivotal to his side's Champions League ambitions.
Celtic host the Dutch champions having failed to pick up any points from their opening fixtures against AC Milan and Barcelona, in what is one of the toughest groups in the competition.
The Glasgow giants reached the last 16 last year and Lennon knows his side need to get some points on the board soon if they are to emulate that achievement.
"We can't lose it, put it that way," said the Celtic manager on whether the match was a must-win or not.
"We are four points worse off in the group than we were at this stage last season. We have a bit of work to do. Home form is important to us, but Ajax are a very good side.
"They will give us plenty to think about, plenty of problems. But we are at home and I think we will be confident enough to take the game to them."
Celtic sit bottom of Group H but have been unlucky not to collect any points so far, losing to two late goals in Milan and a solitary Cesc Fabregas strike for Barcelona in Glasgow.
"There is a frustration that we haven't taken anything from our two games," Lennon admitted.
"But that is significant in itself, given that we played Milan away and Barcelona at home. When you are disappointed after that, you obviously have a good team. And we think we have a good team.
"As I said when the draw was made, we are not the runts of litter. We have been pretty competitive.
"Did we deserve better? Probably. Did we get it? No. There is a lot of emphasis on this game and if we can win it, brilliant. If we get a point, it means we have to go to Amsterdam and win. I think we are capable of doing that."
Ajax were on the wrong side of a 4-0 defeat by Barcelona on match day one before coming close to claiming all three points against AC Milan in Amsterdam with only a last minute penalty denying them the win.
Frank De Boer lost a host of top team stars in the summer, including Derk Boerrighter to Celtic, but Lennon, whose side is also depleted following the departures of Victor Wanyama and Gary Hooper, knows they will still pose a serious threat to his side in Glasgow.
"Siem de Jong is a threat from midfield," said Lennon.
"Viktor Fischer, a young winger they got from Alkmaar, is very dynamic and comes in on his right foot. Kolbeinn Sigthorsson is a striker but he played wide when I saw them against PSV. They are a typical Ajax team, they move it quickly and have good pace in wide areas. They're definitely a threat going forward."
Celtic will be without captain Scott Brown who is suspended after his red card for kicking out at Neymar in the loss to Barcelona while Kris Commons is a major doubt after picking up a hamstring injury in Saturday's 1-1 draw with Hibernian.
Joe Ledley and Australian international Tom Rogic have both returned to training and will be fit to take their place in the squad for Tuesday.