The 36-year-old was dismissed by the Championship club on Sunday for alleged “gross misconduct”. Featherstone say he played three “unauthorised” games for Morley Rugby Union Club and was in breach of the Rovers contract he signed last August.
In a statement, Rovers claimed Griffin had been told “categorically” not to play union.
He was initially suspended in December and then sacked following an appeal last week.
But the player is unhappy with the decision and may take it further. Griffin told The Yorkshire Post: “I am disappointed for it to finish like this and I’ll be taking some legal advice.”
The former Huddersfield Giants, Leeds Rhinos and Salford Red Devils forward declined to comment further but in a message on social media he thanked Rovers’ players and fans and claimed the club acted “inappropriately” and “without due cause”.
Josh Griffin, who plays for Hull FC, has defended his brother on social media, alleging he had permission to play union.
Meanwhile, Tyler Randell is hoping his luck will change after an injury-hit start to his Wakefield Trinity career.
The former Newcastle Knights hooker scored a brace of tries in an outstanding debut against Salford Red Devils last September, but suffered a season-ending leg injury in only his third game for Wakefield, away to Hull.
He made a full recovery from that, but then sustained medical cruciate ligament damage in the opening moments of Trinity’s Boxing Day clash with Leeds, ruling him out of the start of the league campaign.
He said: “The most disappointing thing is I trained all through the off-season, didn’t miss a session, was feeling really good and then five minutes into the first friendly I got injured, but that’s rugby league. It happens.
“I have had two injuries in my last two games, whereas I haven’t been injured for five years I reckon, not a decent injury like this.
“Hopefully all my bad luck has run out now.”