Reportedly, New Orleans wanted Thomas to have surgery on his injured ankle following the 2020 season ... right around the time the receiver began renting the Bel-Air mansion.

But, Michael opted to try to heal the injury on his own ... and allegedly didn't communicate much -- if at all -- with the Saints during that process.

Thomas eventually realized he had to have the surgery -- following all of the drama with his mansion rental he's claiming in the lawsuit -- and he's now expected to be sidelined for at least the first few weeks of the season.

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