A 1-0 home defeat to Barcelona on Tuesday night leaves the Scottish champions at the bottom of their table, one point behind the Dutch side who drew 1-1 with AC Milan in Amsterdam.
It started to go wrong for the the Hoops in the 58th minute when skipper Scott Brown was sent-off for having a swipe at Neymar after fouling the Brazilian star, before Cesc Fabregas scored the winner with a header.
Ajax visit the east end of Glasgow on October 22 before the return game in Holland the following month and the Celtic boss, whose side lost their opener 2-0 to AC Milan in the San Siro, knows points have to be gathered in the double-header.
"I am pleased with the result in Amsterdam because both teams have taken points off each other," he said.
"The double-header with Ajax, if you have any aspirations to qualify, is pivotal.
"Can we take four points or maximum points?
"It is important that we win the next game at home and get points on the board and go to Amsterdam with a positive frame of mind.
"Milan now have Barcelona twice so we have to maximise our opportunities, which we probably haven't done in these two games so far."
Asked about his captain's red card, Lennon said: "I think it is very soft. I have looked at it.
"If any contact, it was minimal. There was a lot more in the game that warranted heavier punishment.
"It was a game-changing decision.
"It is obviously very difficult playing Barcelona with 11 players and even more difficult with 10 but we played very well.
"I don't think the initial tackle was a severe one. It is a physical game.
"I don't think Neymar does himself any favours with way he behaves at times.
"Our supporters are every respectful of great players. Iniesta walks off to a standing ovation from the Celtic support.
"After the incident Neymar gets booed every time he touches the ball."
Barca boss Gerardo Martino was non-committal when asked if Neymar over reacted at the incident when Brown was red-carded.
He said: "I couldn't see with certainty what happened so I don't want to give an opinion.
"But certainly playing with 10 men for 35 minutes against Barcelona is something to think about when analysing the game."