Celtic are three points clear of Inverness at the top of the table and the manager wants 100% focus on Hibernian ahead of Tuesday's Champions League game with Ajax.
Lennon said: "Talking about momentum, the Hibs game is pivotal.
"The players have responded to everything that we have asked them to do in the league but if they want to play on Tuesday night they are going to have to play at their best on Saturday.
"It is there for them and it is another great week for us. The Ajax game is huge in terms of the group and where we want to be in the group.
"I wouldn't say it is a must-win game, but it is a game we would dearly love to win to get us up and running in the group.
"We mustn't lose. I don't like making predictions but if we could get four points out of the next two games it would set us up very nicely indeed. But it is a big ask."
Lennon praised Hibs boss Pat Fenlon for taking the Easter Road club up into fifth place in the table after a tricky start.
"They have turned things around since the Malmo game where it was all doom and gloom and they have some really decent results, winning at Partick and at St Johnstone," he said.
"We lost at Easter Road last year and Pat's teams can be dogged when they want to be and difficult to beat, so we have to be wary of that.
"Paul Heffernan has been a good signing for Pat. I think he is clever, a goalscorer, and they have a threat going forward with him and James Collins while Liam Craig has had an excellent start to the season.
"But we want to go into the Ajax game with a positive result."