The panel decided his challenge to an original three-match suspension was 'frivolous' and added an extra game.
That means Bentley, who was sent-off for a high tackle just 16 minutes into his debut against Warrington Wolves last weekend, will be sidelined until round six of Betfred Super League, missing games against Wigan Warriors, Catalans Dragons, Wakefield Trinity and Hull.
The second-rower was charged by the RFL's match review panel with a grade C high tackle, which normally leads to a ban of two-three matches.
He is the fourth Rhinos player suspended since the end of last season.
James Donaldson received a two-game penalty notice for a dangerous contact in the Boxing Day win over Wakefield Trinity and Blake Austin missed the Warrington match as he served a one-match suspension for a similar offence in a pre-season clash with Hull.
Brad Dwyer was sin-binned against Warrington and handed a one-match suspension which Rhinos decided not to appeal.
Warrington's OIiver Holmes also had his suspension increased after appealing against a one-match penalty notice for a grade B high tackle.
He pleaded guilty to a careless high tackle, but the panel ruled it was reckless and added a further match to his ban for a frivolous challenge.
He will miss Thursday's visit of his former club Castleford Tigers and the round three game at Toulouse Olympique.
Catalans Dragons forwards Dylan Napa and Gil Dudson will miss Saturday's game at home to Wakefield Trinity and the visit to Headingley five days later.
Napa, who was sent-off in last week's defeat at St Helens, was found guilty of grade D striking and banned for four games.
He had admitted a lesser charge of a reckless high tackle.
Dudson, sin-binned in a separate incident, pleaded guilty to a grade D punching and received a three-match suspension.
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