The question of offensive line depth is not a new one for the Eagles in 2015. Entering Training Camp and the preseason, there were questions about who the starting guards would be with Evan Mathis and Todd Herremans no longer around.

Andrew Gardner and Allen Barbre stepped above the competition and secured the starting jobs during the preseason, but now, three games into the regular season, a foot injury has ended Gardner's season and the question of depth on the interior has once again popped up.

The Eagles re-signed Julian Vandervelde on Tuesday morning (which isn’t his first transaction with the team), and he joins Matt Tobin and Dennis Kelly as the most likely candidates to take over for Gardner, with Josh Andrews also in the mix.

"I think both of those guys (Kelly and Tobin), if asked to be there, will do a good job," said offensive coordinator Pat Shurmur. "I think Dennis is a bigger guy. Tobin has good quickness, good job getting to the second level. I would say Dennis is maybe just a little bit firmer at the line of scrimmage, but they are both very good players."

When Gardner left Sunday's game against New York, Tobin was called upon to enter the game, but that doesn't necessarily make him the frontrunner, as Kelly also had starting experience with the Eagles in 2014.

"I thought I did overall pretty well," Tobin said about his first offensive snaps of 2015. "There was an outside zone on my side that I got a little too wide on and got beat inside. There are just a few little adjustments that I need to make."

Tobin, signed by the Eagles as an undrafted free agent in 2013, has the versatility to play both inside at guard and outside at tackle. After playing guard for most of 2014, Tobin played entirely at left tackle during the 2015 preseason, but according to the Iowa product, he's prepared to play inside.

"I got a lot of reps in the offseason at right guard, so I'm a lot more comfortable than I was a year ago. I'm excited to get out there," Tobin said. "I got a lot of reps in between (Jason Kelce and Lane Johnson). I feel like we communicate pretty well."

At 6-8, 321 pounds, Kelly is an intimidating presence along the offensive line, and he's honing his craft each day as he works in his third season in this scheme.

"The first year it was kind of tough to learn the new system plus I was coming off of back surgery," Kelly said. "I think I had a rough time putting it all together and doing everything that they asked for. Then l was taking last year in stride. I got to play a little bit earlier in the season and I just approached it every day by trying to get better, so I think I have been able to benefit from being in the system for three years now. … I feel like I have a pretty good grasp of the run-blocking scheme that we have here. Hopefully it works out and they give me a shot at it."

Like Tobin, Kelly has also has experience playing both guard and tackle, which is undoubtedly head coach Chip Kelly's plan for his reserve offensive linemen.

"I started the majority of last year at guard and then spent preseason at tackle, so it's not like it's a new thing for me," Kelly said. "I'm just making sure I get all the assignments right with the steps and the footwork and the differences of being inside instead and outside."

As for the newly re-signed Vandervelde, he's excited to have another chance to compete between the white lines, but it's always tough to have an opportunity because of an injury to a teammate.

"We're all friends, we're all brothers," Vandervelde said. "Gardner and I roomed together through the whole summer. I know him really well and I feel terrible about what happened. I'm happy to be back, but you never want to come back at the expense of somebody else. Unfortunately, that's the nature of the business."

Whether it's Tobin, Kelly, Vandervelde or someone else who gets the call on Sunday in Washington, the Eagles will look to prove that the question of offensive line depth has indeed been answered.