Neil Lennon concedes that a defeat by Ajax tonight will end his side's hopes of qualifying from the Champions League group stages.

It is a stark illustration of the importance of the contest at Celtic Park, and the pressure that will follow Lennon's side into the tie.

It is not one that the manager or his players will shirk from. Having lost both of their opening ties, against AC Milan and Barcelona without scoring a goal, Celtic need to establish their challenge in Group H before time starts to run out. Lennon will be without the injured Kris Commons, who Lennon hopes will be fit for the return game, but Emilio Izaguirre is fit enough to return to the side and Mikael Lustig will undergo a fitness test later today.

"It's a case of: let's not get beaten," Lennon said. "Losing would end our aspirations of qualifying. We [already] need to win away, because we lost a game here [against Barcelona]. If I want to qualify, we've got to pick something up away, either in Amsterdam or Barcelona. It [a victory tonight] would give us a good chance. I don't want to look too far ahead, but if we can take four points out of the six points, which is a big ask but doable, then we've got a home game against Milan which we can win as well."

Lennon watched Ajax draw 1-1 away to Twente Enschede at the weekend, having also taken in the 4-0 defeat by PSV Eindhoven earlier in the season. He picked out Viktor Fischer and Kolbeinn Sigthorsson as the players who most caught his attention, but overall he expects Ajax to be strong and slick.

"We want to exploit their weaknesses," Lennon said. "I watched them against PSV and Twente, who had really good chances especially in the first half. But Ajax showed a lot of character in the second half, and looked like the home team for long periods of the second half. Ajax have great belief, and they never panic. It's a typical Ajax team.

"Frank is turning them into a real force again.They have great belief in the way that they can play. They'll see this as an opportunity to win the game as well. They'll try to dictate the game as much as they can and we've got to try to combat that.

"We are at home. We want to try to win the game. We will have plenty of attacking options on the pitch. I've got one or two decisions to make. We will see how Mikael is in the morning. He looked okay [yesterday]. There is just one more position we have to debate overnight. It might be in the middle of the park - it might be at left-back. Biram [Kayal] is definitely in contention to start with Scott [Brown] being out. As is [Nir] Biton, as is [Joe] Ledley."

Standing in Lennon's way of a first Champions League point of this campaign is an old foe in the shape of De Boer, who spent six months at Rangers in 2004.

The Dutchman is well aware of the noise generated inside Celtic Park and urged his players to show they have the character to deal with an atmosphere he says is one of the best he has played in. De Boer, who appeared twice at the ground during his short spell in Glasgow, compared the Old Firm derby to the rivalries between Barcelona-Real Madrid and Galatasaray-Fenerbahce, and hoped his young side wouldn't crumble.

"At the derbies between Real Madrid and Barcelona there is a great atmosphere," he said. "But it is also the same between Rangers against Celtic and of course when I played for Galatasaray against Fenerbahce. Those three classics are for me the best in Europe and maybe the world.

"Of course, Boca against River in Argentina is maybe the same but I can say from my own experience that those three classics are unbelievable to get involved in, especially as a player. Our players have to enjoy this kind of atmosphere.

"When you are young you want to play in this kind of stadium with this kind of atmosphere. It can only give you more adrenaline in your body to perform. If you are worse than your normal level then maybe you're not good enough to play at this level. Of course, you can be nervous when the referee starts the game but you must get rid of all the nerves and enjoy a great stadium and great pitch."

De Boer pinpointed Georgios Samaras as the man Ajax need to watch. "Samaras is one of their key players with his strength and height.He's very important. If Celtic can't build the play from the back, the first option will be to go to Samaras and then fight for the second ball. He's so strong at that, it's almost impossible to beat him for the first header. Celtic are then good at winning the second balls and you have to be in the right places for them."

Ajax sit third in Group H with one point from their first two games and de Boer echoed Lennon in his assessment of what a defeat would do his side's hopes of reaching the last 16. "Of course, we would prefer to win the game. If we want the potential to finish in second place then the best thing is to win. That might also put us in a good position for third place. To lose is the worst option."