It happened in the fourth quarter on Sunday, when Tretter finished the game at left tackle after the Packers pulled several starters in the blowout victory.
The NFL announced the fine on Friday.
Tretter said his leg whip was not intentional and planned to appeal the fine. On the play, Tretter's assignment was to cut block on the backside of a pass play to the right. He was penalized on the play.
"I grabbed [Cole] right after the final kneel down to tell him it was totally accidentally," Tretter said Friday. “I didn’t know my leg was even up that high.”
The fine was more than half of Tretter’s weekly salary, which is $29,117.65 before taxes.
The only other Packers players known to have been fined this season were tight end Andrew Quarless ($8,268) for his role in a Week 2 scuffle against the New York Jets, and outside linebacker Julius Peppers (amount unknown) for wearing unauthorized shoes.