The sixth-round draft pick from Michigan State spent most of training camp working with the third-team defense.
Following the final cuts over the weekend and a major knee injury to Jonathan Goff on Monday, Jones seemingly is now the starting middle linebacker for the season opener against the Washington Redskins Sunday.
Jones had a chance to work with the first team for the first time on Wednesday and enjoyed himself.
"It was cool just being out there," Jones said. "It is a different type of motivation. Everybody is so positive and nobody is saying: 'You're only a rookie.' Everybody is just saying you can do this, just believe in yourself."
Jones has no doubts that he can play the MIKE position. He left college as the Spartans' all-time leader in tackles for loss with 46 1/2, and was third all time in tackles with 465. He led the team or tied for team lead in tackles in 31 of his last 39 games.
However, he is taking over for Goff on short notice. Goff injured his right knee running into an offensive lineman in practice on Monday and the team didn't learn he had torn his ACL until Tuesday afternoon.
Jones didn't know about it until linebacker coach Jim Herrmann gave him a call and told him it was time to step up.
"Jon (Goff) always said just be ready," Jones said. "All of a sudden, wow! I didn't see that coming, I feel ready for it."
So do his teammates who put on a brave face with this latest injury. Since training camp opened, the Giants have lost cornerbacks Bruce Johnson and Terrell Thomas with Achilles' tendon injuries, backup linebacker Clint Sintim with a knee injury, second-round draft pick Marvin Austin, a defensive tackle, with a torn pectoral muscle and now Goff, who started all 16 games in the middle last season.
"This is adversity," veteran safety Deon Grant said. "This is the NFL. Dealing with what we're dealing with, I don't think it's happened like that in a long time. I know I can't remember my whole career, but that's adversity. You see what Green Bay went through last year. The next guy has to make sure he picks it up."
Jones is next up at middle linebacker and Grant has been impressed with him.
"Football is his No. 1 priority and he can play," Grant said. "When you got that, that's phenomenal, but he's a (mean) dog at heart, and that's what you need for any kind of player, but especially at that MIKE linebacker."
Linebacker Michael Boley said it felt a little different looking toward the middle and seeing Jones. The only other time he has lined up next to Jones was in walkthroughs.
"I don't think we need to change much with Greg stepping in," Boley said. "He has been pretty steady at that spot in the preseason and made a lot of plays."
It is conceivable that the Giants can come up with a gimmick defense that will allow the team to limit Jones' exposure against the Redskins, much like last season when they used Grant in three safety alignments. If not, safety Antrel Rolle said the defense will have Jones' back.
"Jon Goff was definitely coming into his own. He was controlling the defense," Rolle said. "It's unfortunate we have to move on without him. Greg is going to have to do the job. He is a young guy and now he has to put on his big boy pads."
The Giants had about 10 free agent linebackers in for tryouts, including former Giants Chase Blackburn and Kawika Mitchell. Blackburn, who visited teammates in the locker room on Wednesday, was the backup middle linebacker last season, and their special teams captain.
If Jones starts Sunday, he would be the first Giants rookie defensive player to start on opening day since Barry Cofield in 2006.