It appears Sony Michel’s knee injury is more severe than originally suspected.

The New England Patriots rookie running back is expected to miss the entire preseason and potentially the start of the regular season, as well, as he recovers from the injury he suffered during Wednesday’s training camp practice, sources told Jeff Howe of The Athletic on Saturday.

Michel left Wednesday’s practice early and has yet to return to the field, sitting out each of New England’s last three camp sessions.

Howe initially had reported, citing a source, that Michel was dealing with a “minor knee issue.”

ESPN’s Mike Reiss shed additional light on the procedure Michel underwent:

Michel, the 31st overall pick in the 2018 NFL Draft, has been viewed as a potential replacement for former Patriots running back Dion Lewis, who signed with the Tennessee Titans in free agency. While he still could fill that role upon his return to action, it’s now likely Rex Burkhead will begin the season as the team’s No. 1 back, with James White serving as the third-down back and Mike Gillislee, Jeremy Hill, Brandon Bolden and Ralph Webb fighting for the few remaining roster spots.

This development all but guarantees either Gillislee or Hill will make the 53-man roster, but it’s still unlikely both will stick around unless Michel begins the season on injured reserve.

Though highly productive over his four-year college career at Georgia, Michel’s knee was a concern during the lead-up to the NFL draft.