Sinfield was charged with a Grade C offence for the incident, which saw the England skipper sent off for the first time in his career.
Having submitted an Early Guilty Plea, Sinfield has been banned for two games rather than three and will miss Friday's clash with Salford Red Devils and next week's West Yorkshire derby against Bradford Bulls at Headingley.
In a statement, Rhinos chief executive Gary Hetherington questioned the decision and called for the Rugby Football League (RFL) to be more consistent when handing out punishments.
"Unfortunately this is another example of the pattern of inconsistency displayed by the Review Panel of the RFL," he explained via the Rhinos website.
"Earlier this season, Kris Welham of Hull KR was charged with an unprovoked head butt and received a Grade A charge and no suspension.
"I can fully appreciate the growing chorus of discontent throughout the game with the performance of the RFL in these matters."
Brian McDermott will be able to recall Sinfield for the Challenge Cup semi-final against Warrington Wolves on August 9 as Leeds look to make the final for a fourth time in five years.