A contract season defines a player’s future. Perform well, and he’ll hit free agency poised to make millions as an up-and-coming star. Have a down year or get hurt, and say goodbye to that long-term deal and big signing bonus.

But if history holds for 2016, quarterback Ryan Nassib won’t have much of anything to show at the end of his fourth year with the Giants, the final one on his rookie deal. That’s why these next four games are so significant for him. That’s why this is his contract preseason.

When you are Eli Manning’s backup, that’s usually the only game work you get. Nassib has been on the team for three full years and has appeared in five regular-season games, throwing 10 passes. Even in a league starving for quarterback talent, one in which no-names get megadeals as free-agent saviors, that’s not much of a resume.

Which is why the preseason is Nassib’s only guaranteed time to show the Giants and the NFL that he is capable of becoming a starting quarterback in the NFL.

“I see preseason as my opportunity to show the Giants what I can do,” Nassib said. “Everything we do is a job interview. That’s almost the accumulation of where you can do it on paper, maybe you can do it in practice, but can you do it when the lights are on? That’s pretty much how I see the preseason. Just another part of the job interview for the Giants.”

And, of course, 31 other teams that don’t have Manning on their roster. “That’s something that is kind of in the back of my mind right now,” Nassib said, adding that he is more focused on “the here and the now.”

advertisement | advertise on newsday

Well, it’s here, and it’s now.

The Giants open their preseason Friday night at MetLife Stadium against the Dolphins, and while Manning will take about 15 snaps with the rest of the starters, a good percentage of the rest of the game will be in Nassib’s hands. In past summers he’s done well. His preseason stats include completing 105 of 196 passes (54 percent) for 1,313 yards, seven touchdowns and no interceptions.

“Ryan continues to get better,” Ben McAdoo said. “We have a lot of confidence in Ryan, can’t wait to see him play Friday. He’s going to play a lot of football for us.”

In the preseason, he means. Because if all goes according to plan, even if Nassib is flawless in these four preseason games, Manning will start his 184th straight contest against Dallas on Sept. 11 and take every meaningful snap the rest of the season.

“It’s tough,” said guard Justin Pugh, a college teammate of Nassib’s at Syracuse. “Sitting behind a future Hall of Famer? That’s tough. [But] look how many quarterbacks have gotten their opportunity after playing behind a great guy. The list goes on and on, and those guys get paid.”

The latest on that list is Brock Osweiler, who turned an apprenticeship under a different Manning in Denver into a four-year, $72-million deal with Houston. Matt Cassel, Matt Schaub, Ryan Mallett and Ryan Fitzpatrick have had similar trajectories.

“I hope for the best for Ryan,” Pugh said. “This is a big preseason for him to go out there and show what he can do, and hopefully things work out for him. Hopefully, if it’s not down the road here, he can go get a job and be a starting quarterback. I know he can be a starting quarterback in the NFL.”

Most people with the Giants agree. “If Ryan was ever forced to go in, we would pick up where Eli has left off,” McAdoo said. “We trust Ryan to go in and run the offense. We feel that he can put our players in a position to be successful. We feel that he can go in and do the job.”

As has been the case since the day he was drafted, though, the Giants hope he never has to.