Miller, who missed all of last season with a torn ACL, signed with the Patriots in mid-August. He returned to practice this past week after being on the physically unable to perform list.
"We threw him in the fire pretty fast, just because we're running out of time where you can be very physical in practice," Patriots running backs coach Ivan Fears said Wednesday. "So we wanted to give him a little taste of getting bounced around a little bit. He's done a great job.
"I really expect Lamar to bounce back and be the guy he was, but I'm sure that's going to take a little time."
The Patriots have Sony Michel returning as their top option at running back, but he is still coming back from offseason foot surgery, so he might be limited early in the season.
James White is the top passing back, while Rex Burkhead provides valuable versatility. Damien Harris, a 2019 third-round pick from Alabama, projects to have a significant role once he's recovered from a hand injury that could threaten his availability early in the season.
In addition, undrafted free agent J.J. Taylor (Arizona) is making a charge for a roster spot.
During his three active seasons in Houston, Miller, who signed a four-year, $26 million extension in 2016, ran for 2,934 yards and 13 touchdowns on 716 carries. He also caught 92 passes and scored five touchdowns. Miller's best season for the Texans came in 2018, when he averaged 4.6 yards per carry.
He began his career with the Miami Dolphins, who selected him in the fourth round of the 2012 draft, and has 7,429 total yards from scrimmage in his career and 40 total touchdowns.
ESPN's Mike Reiss contributed to this report.