Detroit Lions center Graham Glasgow walks off the field during training camp practice on Tuesday in Allen Park. (AP photo)

ALLEN PARK — Saquon Barkley mostly stood and watched, resting his strained left hamstring as the New York Giants practiced against the Detroit Lions.

“He’s day to day,” Giants coach Pat Shurmur said Tuesday.

Barkley, a rookie running back drafted No. 2 overall, did some drills very slowly before going to the sideline to work on strength and conditioning. The former Penn State star was in uniform — minus shoulder pads — while his teammates went through the first of three practices with the Lions.

On Monday, he caught a swing pass out of the backfield and was injured either stretching to make the catch or running down the sideline after the catch.

It’s unclear if Barkley will play in Friday night’s preseason game at Detroit.

Jonathan Stewart, who spent the first 10 years of his career with the Carolina Panthers, filled in for Barkley during some snaps with the first-string offense.

The Lions, meanwhile, had a key player walk off the field after being injured. Starting center Graham Glasgow appeared to hurt his left leg. Coach Matt Patricia declined to comment on the injury after practice.

Glasgow started all 16 games last year and played in 15 games, starting 11, the previous year as a rookie.

Detroit is counting on him to improve its running game, which has ranked among the NFL’s worst in recent years. The team’s backup options at center include Wesley Johnson, who started 15 games for the New York Jets last season.