Brentford boss Andy Scott insisted a claim of malicious intent but after allegations made in writing to the FA, a spokesman responed.
"We can confirm that we have written to Rotherham and informed them that we are unable to take any disciplinary action against the Rotherham United player Pablo Mills," a statement reads.
"In accordance with Law 5, FIFA prohibits further disciplinary action from being taken in respect of an incident where it was seen and dealt with at the time by the referee.
"The match referee Mr Karl Evans has reviewed the incident on video and remains of the view that the conduct of the Rotherham United player did not merit a dismissal and the evidence available does not provide sufficient grounds to conclude that the player should have been dismissed."
Douglas added: "We are pleased with the ruling, but everyone at the club would like to reiterate that our thoughts and best wishes are with Nathan and we hope he makes a speedy and full recovery from his injury."