By Joseph Santoliquito

Philadelphia, PA (CBS) — Chip Kelly officially announced on Monday at his day-after press conference that Nick Foles did suffer a concussion on the last play of the third quarter in the Eagles’ 17-3 loss to Dallas on Sunday.

This could leave Kelly in a dilemma. With Michael Vick still nursing a pulled left hamstring and Foles healing from a concussion, Kelly may be forced to start rookie fourth-round draft pick Matt Barkley against the visiting winless New York Giants on Sunday.

“There are a series of tests [Foles] has to go through,” Kelly said. “Nick seems like he’s doing well. There is a protocol and a system we have go through. We know exactly where Matt has to be, where Nick has to be and where Mike has to be, and from there, we’ll make a decision.

“My decision on who the starting quarterback is is going to be based on health, and right now, I don’t know who’s healthy and who’s not healthy. Until we find out who’s healthy, it doesn’t help anybody to say that guy’s our starter. It doesn’t help the situation because I don’t know when they’re all coming back.”

Kelly said he’ll wait until later in the week to determine if Foles or Vick can go. If they can’t, Kelly also opened up the possibility of taking in another quarterback.

After two strong performances against the Giants and Tampa Bay, Foles regressed against the Cowboys, which produced season lows in points (3) and total yards (278).

“I think [Foles] was off a little bit; his feet weren’t set on a couple of those throws,” Kelly said. “There were times when guys were open and he didn’t put the ball on him, and other times we didn’t get off of coverage, and other times when we gave up a little too much leakage with pressure. For one reason or another, we were off.”

Kelly stressed that the Dallas’ man coverage wasn’t the reason the Eagles struggled offensively. He said what Dallas did wasn’t anything they had not seen before. Kelly noted the Eagles had been successful against man coverage.

“The team that played us the most in man was actually the Giants, the Chargers played us a lot in man, the Chiefs played us a lot in man, so it wasn’t something that [we hadn’t seen before],” Kelly said. “The Cowboys actually played less man that the Giants, the Chiefs or the Chargers. I don’t think Dallas did anything drastically different than what we saw in their first six games in terms of how they played. I think they did a good job of mixing their man and zones, but that’s what they had done previous to that. There wasn’t anything new Dallas did just for us. They executed a lot better than we did—I can tell you that.”

Kelly also made sure to laud the work of defensive coordinator Billy Davis, whose defense has improved and held one of the NFL’s better offenses to 17 points. Davis mixed some schemes against Dallas, at times showing blitz and reeling back, and at other times displaying blitz and attacking.

It left Dallas quarterback Tony Romo guessing at times.

“I’ve seen our defense every single week continue to grow and get better,” Kelly said. “I think they have a better understanding of what Billy and that staff over there are trying to do. I always thought the effort was there defensively, but all of a sudden some of the techniques are starting to shine through and everybody is on the same page.”

But when it comes to the Eagles’ offense, Kelly’s offense, he was adamant. He stood by the bromide he’s maintained all season: “We have the mindset here that the only team that can stop us is ourselves.”

Joseph Santoliquito is a contributing sports blogger for CBS Philly.

Watch & Listen LIVE