Sources informed NFL Network, ESPN and the Charlotte Observer of the move Monday. The Panthers will bench Kyle Allen, who has started every game since Week 3. Panthers coach Perry Fewell is expected to announce the move Wednesday.
Fewell replaced fired Panthers coach Ron Rivera two weeks ago.
Allen completed 25 of 41 passes for 277 yards, one touchdown and three interceptions in the Panthers' 30-24 loss to the Seattle Seahawks Sunday in Charlotte, N.C.
The Panthers won their first four games while starting Allen. They are currently on a six-game losing streak and are now out of the NFC playoff picture. Allen completed 62.1 percent of his passes for 3,027 yards, 17 touchdowns and 15 interceptions in his 12 starts, while replacing injured starter Cam Newton.
Grier has not thrown a pass during the regular season. The third round pick in the 2019 NFL Draft completed 55.7 percent of his throws for 385 yards, two scores and three interceptions in four preseason appearances.
The Panthers and Colts kick off at 1 p.m. EST Sunday at Lucas Oil Stadium.