The Millwall striker saw red after a bust up with Gillingham's Charlie Howard less than thirty minutes into the game but the youngster will now have to wait to see if the referee includes the incident in his report. If he does, Grimes will miss the next three games, including the first leg of The Lions' play-off matches.
He will also miss Saturday's clash against Leyton Orient and the last game of the game of season away to Carlisle United, where he was expected to feature at some point.
However reserve team boss Richard Shaw was quick to point out that the red card could have been avoided had the game been refereed better.
"It just needed some sensible refereeing to have avoided that outcome," Shaw told the club's official site after the game. "The referee could have just called them together and told them to cut it out. Instead he decided to take drastic action which could now cost us."
The game ended, which also saw defender Pat O'Connor taken off with a broken nose, ended 1-1.