EAST RUTHERFORD, N.J. -- New York Giants wide receiver Sterling Shepard suffered what is believed to be a serious left knee injury, multiple sources told ESPN, after Shepard had initial tests following Monday night's game against the Dallas Cowboys.

The noncontact injury happened in the final minutes of New York's 23-16 loss to Dallas. A final diagnosis will come Tuesday morning, when Shepard undergoes more tests, but the fear is that his season is over.

Shepard, who was cleared to practice late this summer after tearing his left Achilles last December, leads the Giants with 154 receiving yards through three games. He's also played the most snaps (157) of all the team's receivers.

"It's tough. It's a tough sport," coach Brian Daboll said. "Guys work their butts off to get back from injuries. This is something, if he's out for the whole season, which we'll probably know [Tuesday] morning ... you hurt for those guys because you watch them in the rehab room, you watch them in the offseason. It's just a shame."

Shepard, 29, had been shouldering a big workload early this season. He was given a maintenance day Wednesday as a result.

The injury occurred on the Giants' final offensive play Monday night, when Shepard was jogging near the right sideline. He limped onto the cart and players from both teams came over to offer words of encouragement.

"It's tough. I'm not even going to lie. It's hard not to get choked up about it," Giants wide receiver Darius Slayton said of seeing the injury. "He's been here since the first day I got drafted. He's done a lot for me as a young guy. And then seeing him come off the Achilles last year and rehab all year, and how hard he fought to get back out there, it's definitely hard to see."

The play resulted in what was essentially a game-ending interception. In the moment, that hardly mattered.

Shepard was on the ground writhing in pain.

"It's hard," said running back Saquon Barkley, one of Shepard's best friends on the team. "I would say I'm one of the biggest competitors, but when I saw Shep was down, I was like, 'What the heck is happening?' Obviously I realized it was a pick, but in that moment, you see him on the ground, I didn't even want to walk over there. I dropped, said a quick prayer and ... it's tough. He's been through a lot of injuries recently, it's tough to come back and battle the way he has, from an Achilles, and to go down on a play like that, it's a tough way to end an emotional game."

The Giants (2-1) lost for the first time this season and for the 10th time in 11 tries against their division rivals.

Shepard has been around for a good chunk of those losses. He is the longest-tenured Giants player. He's been with the team since being selected in the second round of the 2016 NFL draft out of Oklahoma.

The veteran receiver took a pay cut this offseason to remain in the area and with the Giants. This is the latest blow to a career that has veered off track in recent years.

"Hate to see that for him," quarterback Daniel Jones said. "No one deserves that, but especially not him. He works his tail off and means a ton for this team, for all of us."

Shepard has consistently produced for the Giants. The problem is that he hasn't been able to stay on the field.

This will likely be the fourth straight year he's missed at least four games because of injuries. He's dealt with Achilles, quad, hamstring, toe and concussion injuries in the past few years. Now, it's his knee.

"I just feel terrible for the guy," Daboll said.

But Shepard was able to get back from the Achilles injury in just over eight months. He looked good at practice late this summer and returned to game action for the season opener against Tennessee on Sept. 11. He caught a 65-yard touchdown in that contest.

Shepard has 362 career catches for 4,038 yards and 22 touchdowns.