Frank de Boer acknowledged Ajax are under pressure to beat Celtic in the UEFA Champions League following a stuttering run of form.
Ajax have picked up just one point from their opening three group games and were beaten 2-1 by Celtic at Parkhead a fortnight ago.
The Dutch champions are also struggling domestically and a 1-0 home defeat by Vitesse Arnhem on Saturday saw Ajax slip to sixth in the Eredivisie table.
De Boer conceded the departures of Christian Eriksen to Tottenham and Toby Alderweireld to Atletico Madrid in the summer have weakened Ajax, but he is hoping confidence will return for Wednesday's home date with Celtic.
"How big is the match? Well, if we want to have a meaningful say in this group, we must get three points, that's clear," said the Ajax coach.
"It would take us a point ahead of Celtic. Also, if we presume Barcelona beat AC Milan at home, we can still have a chance of second spot.
"For Celtic, a draw may be enough and they'll go into it more confident than us as we're the team under pressure right now.
"The result against Vitesse is a concern but I'm sure the confidence will return because we have a lot of quality. I will keep telling them that.
"Also, the way we played in Glasgow also gives me belief.
"The Vitesse result was a mental slap for us as we were so close to getting something. It is a blow but we made a clumsy mistake and they punished us.
"We have ambitions at this club but I've always said it's difficult when our best players leave us.
"Siem De Jong stayed in the summer but Christian Eriksen and Toby Alderweireld have gone. When that happens, you take a step back - perhaps two steps."