The reason is because of migraine headaches, according to a source.
Shepard missed Sunday's win over the Kansas City Chiefs and has not practiced this week. He tried to do some light running this week, but the migraines returned.
A source told ESPN's Jordan Raanan that Shepard felt "better" on Wednesday, and he made the trip with the Giants to Maryland in hope of being active Thursday night.
Shepard, a second-year receiver, has posted 38 receptions for 475 yards and one touchdown this season. He leads the Giants in receiving yards in 2017 on a unit that has dealt with numerous injuries.