Giants first-round pick Justin Pugh is out indefinitely after suffering a concussion in practice Thursday, Tom Coughlin revealed today.

Pugh, an offensive tackle from Syracuse who is battling veteran David Diehl for the starting job on the right side, is going through the NFL’s concussion protocol and won’t return until he is cleared by an independent neurologist.

Coughlin wouldn’t say much about the injury except to say that Pugh “took a shot to the head” late in the indoor workout Thursday and was diagnosed with a concussion shortly afterward.

The injury comes at an inopportune time for Pugh, who was taken by the Giants 19th overall last April. Pugh had been getting an increasing number of snaps ahead of Diehl with the first-team offense until suffering the concussion.

bhubbuch@nypost.com