An official announcement is expected Wednesday.
Second-year quarterback Kyle Allen has been the starter since Cam Newton was sidelined with a Lisfranc injury after a Week 2 loss to the Tampa Bay Buccaneers. Allen won his first four starts and five of his first six to help the Panthers to a 5-3 record.
Carolina has lost its past six games to fall out of playoff contention. Allen has thrown 11 interceptions to only eight touchdowns during that stretch. He had three interceptions and one touchdown during a 30-24 home loss to the Seattle Seahawks on Sunday.
Interim coach Perry Fewell stood by Allen a week ago, saying he would be the starter against the Seahawks despite throwing two interceptions during a 40-20 loss at the Atlanta Falcons.
Fewell was noncommittal Monday when asked if he might start Grier over Allen, saying he was evaluating the position.
"Probably make that decision on Wednesday," said Fewell, who replaced fired coach Ron Rivera two weeks ago. "Over the next two days we'll evaluate and you'll know on Wednesday."
Fewell's immediate assessment of Allen's performance against Seattle didn't bode well for the QB keeping the job.
"I do believe there were plays out there to be made, and at times he didn't make those plays that needed to be made," Fewell said. "That goes along with the position of being a quarterback. That's what we're looking at right now. Did he have enough protection? Smart decision-making? So we'll evaluate that and see.
"I thought he did some solid things, and then obviously not some good things."
Allen admitted after the loss he wasn't doing enough to help the Panthers (5-9) win like he did during a 4-0 start, when he didn't throw an interception.
"The only thing that is different is I'm just turning the ball over more," Allen said when asked to compare what is happening now compared to his initial starts. "Decision-making hasn't been as good, I guess. I just need to start putting us in a solid position to help win the game, because what I'm doing now is not helping us to win the game."
Allen declined to comment on Monday.
The Panthers had hoped to treat this like a redshirt season for Grier, selected out of West Virginia with the 100th overall pick. That was before Newton's injury, Allen's struggles and Rivera's firing.
Fewell said he felt before Sunday and even during the loss that Allen gave the Panthers the best chance to win. Allen led a rally from a 30-10 deficit to a one-score game before throwing his third interception with 2:55 remaining.
Fewell said Grier has shown improvement running the scout team the past few months. Now he'll get his chance running the Carolina offense, something he has done on a limited basis since training camp.
"He's gotten better with command of the huddle," Fewell said. "When I see him on the look squad, his voice inflection is good because we ask him to do some hard counts. We've asked him to do some things the opponent's quarterbacks will do. His ability to scramble and throw on the run has gotten better.
"So he's progressing as a rookie. He's not there yet, but he's progressing."
Grier, who finished fourth in the 2018 Heisman voting, played two seasons at West Virginia after spending 2015 at Florida.