"The most important thing is to blossom on the pitch. I could not anymore. And a year and a half is a long way to go when you have hard days," Landreau, who was contracted until 2014, told a news conference after Lille had earlier announced that club and player were going their separate ways.
"I have freed myself both sportingly and psychologically," he said.
"I was told months ago that I was not involved enough...I was not considered by the club's manager as an example, or as someone good for the rest of the squad. I took note of that, I spoke to the coach (Rudi Garcia) but he did not take sides," Landreau said.
The experienced keeper, who has made 568 league appearances for Nantes, Paris St Germain and Lille, was a key player when the Northerners clinched their first league title in more than 50 years in 2011.
Capped 11 times by France, Landreau spent three and a half years at Lille, with whom he also won the French Cup in 2011.
"When he told us that he wanted to leave, we agreed because we have thought it was the right decision," Paquet told a separate news conference.
Garcia added: "We have to move forwards with the players committed to the team project. We had two very good goalkeepers, we have one left," he said, referring to second choice Steeve Elana, who was signed from Stade Brest in the close season.
Lille, 10th in Ligue 1, play away at Sochaux on Saturday (1900).