Rose, 27, believes that 24-year-old Scotland international midfielder McGregor played for the penalty during the Scottish Premiership game between the two sides.
Brendan Rodgers’s Celtic played out a 1-1 draw with Motherwell away from home at Fir Park in the league on Wednesday evening.
An own goal from Mikael Lustig saw the home team take the lead in the 78th minute, but Scott Sinclair restored parity from the penalty spot on 88 minutes after Rose’s challenge on McGregor had been deemed to be a penalty.
“I don’t think it was a pen,” Rose told The Glasgow Evening Times. “In the box I have an awareness if he was going to commit and get to the ball first. But I’ve seen it back, I’ve planted my leg and he’s just ran into me and flopped over.
“When the ref blew the whistle, I was shocked. It’s a tough job of course, but for me it was definitely not a penalty.
“Did he play for it? Clearly. Of course. He’s gone down, and I think it was really soft. You see players going down in the box a lot and it’s happened twice to us in a week now.”
Over the course of the 90 minutes at Fir Park on Wednesday evening, hosts Motherwell had 49% of the possession, took five shots of which one was on target, and earned four corners, according to BBC Sport.
Visitors Celtic had 51% of the possession, took 21 shots of which seven were on target, and earned seven corners, according to BBC Sport.