That leaves Mac Jones and Bailey Zappe on the depth chart, with coach Bill Belichick yet to announce a starter for Sunday's road game against the New York Giants after he had benched Jones late in the team's most recent game -- a Week 10 loss to the Indianapolis Colts in Frankfurt, Germany.
Jones and Zappe split repetitions in practice this week, according to a source, with Grier the clear-cut No. 3 option. The Patriots also have former Louisville quarterback Malik Cunningham on the practice squad, but he has been working more at receiver since joining the team as an undrafted free agent in May.
As for Grier, the Patriots had signed him off the Cincinnati Bengals practice squad Sept. 23, with Belichick citing the importance of depth at quarterback over the course of a long season.
Grier didn't appear in a game for the Patriots, serving in the role of emergency quarterback for seven games.
In somewhat of a surreal scene in the Patriots' locker room Tuesday, Grier was mobbed by reporters given the uncertainty surrounding the team's plans at the position.
"My role my entire career has been to be ready," he said that day. "Injuries happen. You've seen around the league, a lot of guys had to step up and be ready to play, and if I have to, I'll be ready to go."
The Patriots are likely to use Grier's roster spot for much-needed offensive line help, as tackle Conor McDermott is out of practice squad elevations and veteran tackle/guard Riley Reiff could potentially be added off injured reserve.
The Patriots are 2-8 and in last place in the AFC.