The prop, 28, will miss Sunday’s Qualifiers opener at Super League Hull KR for an undisclosed issue.
Coach John Kear insisted: “I’m not worried by it - not at all.
“But we decided to take a stand.
“I’d think he’d be gutted at missing out but you’d have to ask Keegan that.
“It is because of an internal disciplinary matter and it’s one game. That’s it as far as we’re concerned.
“He’ll miss Hull KR and then be involved again for the rest of the Qualifiers.”
Batley-born Hirst is the first openly gay player in rugby league after coming out last year and has spoken of how the decision helped him find some of his best career form this season.
He helped unfancied part-timers Bulldogs to third spot in the Championship against all odds - setting up the Middle Eights clashes with Super League opponents such as Hull KR, Huddersfield Giants and Leeds Rhinos.
The ex-Hunslet Hawks, Featherstone Rovers and Dewsbury Rams forward is currently dating Coronation Street actor Antony Cotton, who plays Sean Tully in the ITV soap.