Laurent Blanc's men claimed a 3-1 win at Lille on Sunday to break the points record in the league with 86.
The title was sealed by PSG on Wednesday, and Ibrahimovic said his team were struggling to stay interested late in the campaign.
"It's not easy to play when you are champions already," the Swedish striker said
"In the game, the pressure's not there and you start to relax. And I think the motivation went down a little bit after the Champions League but we won the cup final.
"Monaco helped us win the championship and now we are the champions. So, we play the two games because we have to play them."
Ibrahimovic was unable to get on the scoresheet on Sunday, but with 25 league goals is nine clear of the next best in France's top flight.
He said his conditioning was still behind as he continued his return from a hamstring injury.
"A good game. We won 3-1. I played the whole game and I was feeling very good," Ibrahimovic said.
"I'm not in the condition for 90 minutes but everything was good, we took the three points. I think we beat some kind of record, most points in the competition. I didn't know but now I know."
