Philadelphia still has three more preseason games before it must answer the question of who will be on the 53-man roster, but Friday's opener did teach us a few things about not only what to expect, but what is still very much in doubt.

Three things we learned:

1. We still don't know who will be the team's starting quarterback.

Sure, Nick Foles was the first quarterback off the bench Friday, replacing Mike Vick beginning with Philadelphia's third possession, but remember that this week, Foles will take the first snap with the Eagles' first-team offense on Thursday against Carolina (Listen on 97.3 ESPN).

Vick has ten years of experience playing in the NFL and Vick's first game in the Eagles first preseason game his first two throws were pinpoint darts to the intermediate and deep levels, the first for 22 yards to Jason Avant down the seam and the second good for a 47-yard scoring bomb to DeSean Jackson, over the top of Aqib Talib.  It reminded you of how well he can throw the ball when he's not getting constant pressure like he did for much of 2012 behind the Eagles porous offensive line.

Foles completed 5-of-6 passes for 43 yards, scrambled once for ten yards and did fumble one time.  While he didn't play poorly by any means in the preseason opener, Vick was pretty much perfect.

“I thought they both did a good job," Eagles head coach Chip Kelly explained.  "Nick unfortunately had that fumble on the series when we had the protection breakdown, but he came back and put a pretty good drive together. They both got us into the end zone, so I was pleased with how those guys played.”

2. Greg Salas has everyone's attention.

Jeremy Maclin's injury will open up a job for one of these receivers, and Salas made a pretty compelling case why it should be him, leading Philly in receiving (3-54) in the preseason opener and securing a 12-yard TD from Matt Barkley.  It wasn't just the statistics, but the fact that in camp Salas has stood out. .

"He’s one of those guys that just keeps showing up," said Kelly. "He made a catch like that two days ago against the Patriots on the sideline. He’s that guy that whenever he gets his opportunity, he seems to step up. That’s an important thing, because depth at wide receiver is a huge question for us right now. But you have a guy that has a little experience, and that showed today. He kind of has a knack for making plays. Every time you get a chance to get on the field, you’re building your resume, and he keeps building his resume and showing up, and everybody will take notice of him.”

Salas has been with a pair of teams, the Rams and Patriots before landing here with the Eagles, but he knows he still has more to prove before he makes the roster.

“It doesn’t really mean much until it’s the regular season," admitted Salas.  "But it feels great to get out there and make some plays.”

3. Philadelphia is as good – and deep – as advertised at running back.

Eagles starting running back LeSean McCoy might not have played on Friday night, but his replacements showed they are more then capable fill-ins should McCoy get hurt.

And for all the attention that has been paid to Chris Polk's performance through the first two weeks of training camp, it was Bryce Brown who really stood out Friday. He's physical and relentless and the way he broke on tackles rushing five times for 22 yards and a touchdown and caught two passes for 19 yards in the Eagles' preseason opener, it made you wonder how many teams in this league Brown would be starting for.

“I think those guys are a lot like the quarterbacks," Kelly said about the competition at running back.  "I wouldn’t read too much into who played first. I thought Bryce played really well tonight, and Chris has played really well in camp and did some nice things. We feel like besides LeSean [McCoy], we have a couple of guys that can play, so we really were just rolling those guys.”

The only bad news: Polk rushed four times for only seven yards and didn't show the ability to turn nothing into something.

Three things we're still trying to figure out:

1. Just what to make of Greg Salas's debut?

He was productive, logging 54 yards on three catches and a touchdown, but the majority of that came in the fourth quarter when Philadelphia was playing against the nether regions of the Partiots' defensive depth chart. No doubt about how well Salas played on Friday, and he showed he can make some tough catches, and has so far in training camp

"He has," Kelly said.  "But I think if you watch him practice against the Patriots, he made big plays and he just keeps picking it up."

The next three games will provide a better idea of how he'll fare against the upper rungs of an opposing defense - if in fact he has moved up the Eagles depth chart, he had some time with the Eagles first team Sunday at practice.

"I thought Salas was the one guy in that after the first three (receivers) that really stood out to us," Kelly stated.

2. What should we make of the Eagles 3-4 front alignment?

The Eagles did manage to get three sacks of Patriot quarterbacks and hit the quarterback 10 times during the game.

But at the same time, the Pats ran the ball right at the Eagles to the tune of 31 times for 248 yards and three touchdowns, New England averaged eight yards per carry.

"Some of it is the whole system's new," Kelly explained.  "It was first live action in a game.  We haven't had live football since we've been here, so it was our first time."

3. How serious is Jason Peter's injury?

He didn't play in Friday's exhibition game, which is hardly shocking after he has been sitting out since last Wednesday with a hamstring issue. He finally was seen on the practice field today at Lincoln Financial Field.

"Jason was running today," Kelly stated.  "He's made improvements and strides.  But if he doesn't practice, we're not going to play him on Thursday.  So we'll see how he recovers too."

Remains to be seen if this is going to be yet another injury that slows Peter's development, The Eagles are depending upon him to be ready to start at left tackle, there's no doubt that his unique power at 340 pounds could really elevate the level of play from this offensive line that was a total weak spot in 2012 without him.