But Agnew would be a candidate to be activated off injured reserve later this season if Detroit is making a playoff push, according to a source.
The Lions received better news on veteran guard T.J. Lang, who is showing signs of improvement after suffering a concussion last month, according to a source.
Despite suffering at least five concussions since 2015, Lang is feeling better and is no longer experiencing any fogginess, according to the source. If he passes his baseline test this week -- and there is optimism and an expectation that he will -- Lang would be expected to play next Sunday at Miami after Detroit's bye this week.
Agnew, 23, was an All-Pro as a rookie last season, when he scored two touchdowns off punt returns and averaged a league-best 15.4 yards per punt return. The Lions signed linebacker Trevor Bates to replace him on the roster.
Lang, 31, suffered his most recent concussion on Sept. 30 against the Dallas Cowboys and did not play last week against the Packers. The two-time Pro Bowler had been working through a back injury throughout the first few weeks of the season and dealt with a foot injury during training camp.
ESPN's Michael Rothstein contributed to this report.