How soon will Saquon Barkley be able to contribute?

He came to the Giants with a big-time reputation, a spotless resume and an unbridled enthusiasm befitting his irresistible personality. Yes, Saquon Barkley cannot wait for things to get started.

The former Penn State running back probably was the easiest player in this year’s draft to evaluate, and Giants general manager Dave Gettleman knew early on that this would be his guy at No. 2. Once Gettleman concluded that  Eli Manning still had some good years left, Barkley became the target.

And now his moment is almost here.

Next Sunday, Barkley will live out the dream he harbored while growing up in the Bronx and  eastern Pennsylvania. He will take the field at MetLife Stadium for the Giants’ opener against the Jaguars, and he will do as his childhood idol, Curtis Martin, did for the Jets on all those football Sunday afternoons. There will be excitement. There will be nervousness. There will be anticipation.

But the fact is that Barkley enters Week 1 of the regular season under less-than-ideal circumstances.

Barkley’s foray into the NFL began with a 39-yard run off right tackle in the preseason opener against the Browns on Aug. 9. The play offered a tantalizing hint of what was to come from the big-time running back, and even his next four runs —  which totaled a measly four yards combined — couldn’t dampen the enthusiasm about the rookie.

But that was the extent of Barkley’s live action in the preseason, thanks to a hamstring strain he suffered in a joint practice with the Lions on Aug. 13. He missed eight days of practice, and the timing of the injury forced him to miss the remainder of the preseason. Which means the sum total of his exposure to the speed of NFL football is the five carries he had in the first half against the Browns.

“Obviously, I would love to be out there and play as quickly as I possibly can,” Barkley said upon returning to practice. “But that’s part of the game. When I’m able to play, I have to be 100 percent ready.”

The good news is he appears fully healed from the injury, as the Giants did right by him by not playing him the final two games. No sense having him re-injure the hamstring — which happened to Odell Beckham Jr. in his rookie season and prompted a four-game absence at the start of the 2014 season. Better to keep him out of harm’s way in the starters’ final dress rehearsal against the Jets last weekend and  the finale against the Patriots on Thursday  night,  when backups played for both teams.

The better alternative, of course, would have been to give Barkley a bigger dose of playing time to get him  acclimated to the speed of the pro game. There’s no replacement for playing, and practice  gets you only so far, especially in the controlled atmosphere of today’s NFL. With so few padded practices  permitted in training camp, Barkley has had to build much of his early foundation with mental reps and less-than-full-speed drills.

Complicating matters further is the poor preseason performance of  Jonathan Stewart, who was brought in to be a mentor for Barkley as well as a backup. The 31-year-old Stewart looked old and slow when he was in the lineup, and he lost a fumble against the Jets. Stewart has insisted that there is nothing to worry about and that he’ll be ready to start the season. But with Barkley seeing only limited action, coach Pat Shurmur will have to be judicious in figuring out an appropriate workload for the rookie. Second-year tailback Wayne Gallman, who had a fine preseason, might be leaned on more than Shurmur had anticipated coming into training camp.

“There’s some guys that don’t take as many reps as they would like and still have to go out there every single week and produce,” Barkley said. “I have to take that mindset.”

Barkley believes his intensive study of the Giants’ offense will serve him well. There is more to be done, though.

“Some people learn better on the field, some people learn better just from watching film and studying the playbook,” he said. “For me, I kind of do a little bit of both. I like learning the playbook, learning on film and watching film and then go out there, doing it full speed.”

He hasn’t had that luxury since the Browns game, and  he admits he needs to brush up on the finer points of the playbook.

“I’m not going to sit here and lie and say I’m 100 percent perfect with the playbook,” he said. “I’m still a rookie. I’ still have to get better in that area.”

Barkley’s teammates don’t seem worried about any residual impact from the layoff.

“He’s a guy that works really hard,” linebacker Alec Ogletree said. “He doesn’t act like a rookie. He’s a student of the game. He asked a lot of questions, and he’s always willing to learn.”

Manning can’t wait to have him on the field and is especially looking forward to utilizing Barkley’s receiving skills.

“That’s what makes him special, the fact that he can be a receiver out of the backfield,” Manning said. “It just makes him that three-down back, finding ways to get him the ball in space. That’s a matchup we like. If we get man-to-man, that’s a matchup we like in the mix. Getting him the ball and letting him be an athlete, get the ball to him in space where he can make guys miss and get some big gains for us.”

So many possibilities for the rookie running back. The Giants are about to find out how much he can add to their offense.

And after a preseason with precious few opportunities, how quickly he can do it.

By Bob Glauber

Special to NewsdayBobGlauber

Bob Glauber retired in 2022 after covering the NFL for nearly 40 years. He was selected in 2021 for the Bill Nunn Career Achievement Award by the Pro Football Writers of America, and is a three-time winner of the New York State Sportswriter of the Year by the National Sports Media Association. President of the PFWA for the 2018-20 seasons, he is the author of “The Forgotten First” and “Guts and Genius.”