The Patriots designated Thornton (collarbone) to return from injured reserve Wednesday, Jeremy Fowler of ESPN.com reports.
The transaction opens a 21-day window for the rookie to practice with the team before New England would have to add him to the active roster or keep him on IR for the remainder of the season. He can return as soon as Sunday's game against the Lions if he's deemed healthy, but Thornton likely will start off in a part-time role when he first joins the New England offense.