It seems pretty clear from his press conference that this point that the ankle problem is real. That it was a real injury sustained during the Chargers game. That it's kept him from practicing, and that he feels it will be fine for the game.
Sometimes a cigar really is just a cigar.
Brady also seemed to imply that at least one of the picks in the SD game was the result of the ankle, when he said something to the effect that he couldn't blame the first one on the ankle.
It also seems there is zero possibility that the walking cast was a put on or deliberate. Brady seemed genuinely unhappy and surprised about the paparazzi when he went to New York and disappointed that his place of "refuge" was blown.