The Eagles said Foles suffered a shoulder strain, and the reigning Super Bowl Most Valuable Player told reporters after the 37-20 defeat that he was "optimistic" about the severity of the injury.
"It just sort of got jarred in a funny way as I was following through, but you know it feels good and we'll check it out more thoroughly," said Foles.
With starting quarterback Carson Wentz still rehabbing from a torn ACL that ended his 2017 season, any injury to Foles is reason for heightened anxiety for the defending Super Bowl champions.
Foles already missed the preseason opener and some practice time due to neck and back spasms, but Philadelphia coach Doug Pederson was taking a cautious approach on his quarterback.
"Listen, I am going to wait until I speak to my doctors tonight, tomorrow," said Pederson after Thursday's game. "We will get a good evaluation on him and I will definitely keep you updated as we go."
Foles was hurt on a strip-sack by New England's Adrian Clayborn. The loose ball was picked up and returned for a touchdown by Ja'Whaun Bentley. Foles dropped to one knee after the hit and was clutching his arm above the elbow.
"I was getting ready to throw a deep ball and it got grabbed as I was following on through so it sort of got a little strained," said Foles of the play. "But it feels alright, feels pretty good. Hopefully there's no issues."
Foles departed after the injury with the Eagles trailing 17-0 in the rematch of Super Bowl LII. He completed 3 of 9 passes for 44 yards and was sacked three times.
"It wasn't good but at the end of the day, it felt good to be back out there," assessed Foles. "I missed on some throws but was starting to get a rhythm and get a feel back and that takes time. That's why we have the preseason, to go out there and play and it wasn't good enough. I have to be better."
Pederson was not overly concerned about the performance of Foles, acknowledging that he had trouble with his accuracy.
"I think he had some plays that he would want back and we would want back as an offense," said Foles. "And we just got to continue to work, you know. It's part of the game. We have to make the corrections, you know, this next week and get ready for our next one."
Foles did stick around and met with Patriots quarterback Tom Brady after the game. Brady, a five-time Super Bowl champion and MVP of the game on four occasions, failed to shake Foles' hand following the Super Bowl victory and the subject has been brought up repeatedly during the offseason.
"I think everyone's made a big deal about it. I don't think Tom and I think -- you know, there's a lot of craziness," said Foles. "I've always respected Tom, I met Tom several times and it was great to see him. But like I said, I think everyone made a bigger deal because at the end of the day, he's a great dude. He's a heck of a player, one of the greatest of all time and you know, to say hi, that's what quarterbacks do after games.
"I know everyone made a big deal of the Super Bowl but the Super Bowl's chaos after. But he was nice, as he always is, so I wished him the best of luck this season."