Ashton, who last month became the first player to score 100 tries in the English Premiership, was shown a red card for a high tackle on Harlequins' Cadan Murley in Leicester's 20-17 defeat on Saturday.
Leicester face Sale on Sunday and Ashton will be available for the game as well as the final on May 27th at Twickenham if they reach it.
"Mr Ashton accepted committing an act of foul play that would have merited a yellow card," panel chair Gareth Graham said in a statement.
"The panel concluded that there was indirect contact to the head and that any force to the head/neck was low. Consequently, the panel concluded that there was not a high degree of danger."
Ashton, who scored 20 tries in 44 test appearances for England between 2010 and 2019, had announced his retirement from professional rugby at the end of the season, ending an 18-year career.
He started in rugby league with his home-town club Wigan before switching to union with Northampton in 2007.
