Gregor will take charge of the Warriors for the last time when they host Edinburgh on Saturday before taking over as Scotland head coach.
The 1872 Cup is the only silverware that will be at stake this weekend, with both sides out of contention for the PRO12 play-offs.
And Peter says it's not the way the players wanted to mark the departure of the head coach who took Warriors to the European quarter-final and the PRO12 title during his five-year stint at the helm.
Speaking to the press ahead of Saturday's game, Peter said: "It's a shame the way the season has gone. It just doesn't sit right with me the way the end of the season has come around. It doesn't feel right that we don't have a semi-final to look forward to.
"We've got no one to blame but ourselves. We've just not played well enough. We've under-performed and not done ourselves justice.
"It's a bit horrible the season is coming to an early end but it will just make us hungrier to get back to work.
"It's hard to put into words what Gregor has done. He's taken us to another level.
"We've gone from having a thousand people watching us at Firhill if we were lucky to selling out Scotstoun every single week regardless of who we are playing."
He added: "With the brand of rugby we've been playing, Gregor has been tipped for all sorts of jobs.
"Over the last two or three years every club has been after him at one point and that's testament to his dedication in preparing us.
"It's just disappointing we don't have the play-offs there to send him off on a proper high."