Gress, 6-7 and 300 pounds, is a rookie free agent from Penn State, where he played in 32 career games with 12 starts. As a senior in 2013, he started eight games as part of a three-man tackle rotation with Gary Gilliam and Donovan Smith.
Gress is the third offensive lineman signed by the Giants since training camp opened last week, joining John Sullen and Mark Asper.
The western Pennsylvania native earned degrees in both telecommunications and journalism at Penn State.
Kropop, a four-year veteran, was signed by the Giants on Jan. 7. He recently suffered a foot injury in practice.