Celtic are "extremely disappointed" over Ryan Christie's three-match ban after he was found guilty of grabbing Alfredo Morelos by the genitals.
The Scotland player, 24, was charged with violent conduct following Celtic's 2-1 loss to Rangers on 29 December.
A hearing on Monday upheld a two-game ban, with a further one added due to a previous red against Livingston.
The Scottish Premiership leaders said the sanction "demonstrates a worrying lack of consistency".
Midfielder Christie will miss the Scottish Cup tie with Partick Thistle and league games against Kilmarnock and Ross County later this month.
However, he was a doubt for those fixtures after
undergoing groin surgery due to an injury sustained in the final Old Firm match of 2019.
Christie had been booked by referee Kevin Clancy earlier in the match but escaped punishment over the incident with striker Morelos.
This time last year, Celtic claimed Christie was the victim of a similar offence - at the hands of Morelos - in Rangers' 1-0 Old Firm win last Christmas, but the Colombian did not face any sanction.
And Celtic said in a statement: "Given the recent treatment of Celtic players and the lack of sanctions being imposed on those responsible, the fact that a sanction has been imposed on Ryan for the incident in question demonstrates a worrying lack of consistency in the Scottish FA fast track process.
"Naturally, we will be contacting the Scottish FA regarding our concerns. Scottish football deserves a disciplinary process which is fair, consistent and fit for purpose.