He may not regret it now, but Earl Thomas will end up wishin' he didn't throw the ol' single barrel salute to his team last Sunday ... his ex-Seahawks teammate Walter Thurmond tells TMZ Sports.
Earl had been SUPER pissed about not getting a new longterm deal from Seattle this offseason, but decided to play anyway ... and promptly broke his leg against the Cards.
That's when Thomas -- bitter about the whole situation -- threw up the one-finger salute to Pete Carroll and Co. ... something Thurmond says the All-Pro safety will regret.