Mark Sanchez will be the Eagles' starting quarterback for more than a month after Nick Foles broke his left collarbone in Sunday's 31-21 win over the Houston Texans.

Foles will not require surgery, according to a league source, but he will be sidelined at least six to eight weeks.

That opens a spot for Sanchez, who was once the franchise quarterback with the New York Jets before he was benched, injured, and eventually released last spring. He has found new life under Eagles coach Chip Kelly, who is confident that Sanchez can be a capable replacement for Foles.

"I feel great about Mark," Kelly said Monday. "I thought he's done a great job in our system. I thought he played outstanding in the preseason and showed no rust or anything when he got in there against Houston yesterday.

"So we feel real confident and feel obviously very bad for Nick that he's out, but I feel very confident in Mark."

Foles underwent an MRI exam Monday for further evaluation of his broken clavicle. Green Bay quarterback Aaron Rodgers suffered a similar injury last year and also avoided surgery. He missed seven weeks.

The Eagles will play Monday against the Carolina Panthers. Then they visit Green Bay, host Tennessee, and play at Dallas on Thanksgiving before visits from Seattle and the Cowboys. That six-game stretch brings the Eagles to Week 16, which likely would be the earliest Foles could return.

That means any hope of the 6-2 Eagles' reaching the playoffs this season - and perhaps even playing deep into January - depends on how Sanchez performs as the starter.

Sanchez completed 15 of 22 passes for 202 yards with two touchdowns and two interceptions in three quarters of relief on Sunday. It was his first action since the preseason, when Sanchez excelled. He went 25 of 31 for 281 yards with two touchdowns and an interception in parts of three games.

Sanchez, a 6-foot-2, 225-pound Southern Cal product, was the No. 5 overall pick in the 2009 NFL draft and started 62 regular-season games and six playoff games in New York. Turnovers, injuries, and the lack of offensive talent around him ultimately dimmed Sanchez's stardom.

It did not matter to Kelly, who has known the quarterback since Sanchez was a high school prospect at Mission Viejo (Calif.) High. Kelly called Sanchez a "hell of a quarterback."

"I think he obviously has a big-time arm, an NFL arm, he's got NFL feet," Kelly said. "He's really, really smart. . . . Great work ethic, very athletic, all the things you're looking for in a quarterback."

Kelly insisted that he adapts his offense to the quarterback's skill set, so the Eagles can adjust the system to what works for Sanchez. The quarterback is comfortable playing up-tempo, which is a necessity under Kelly. The offense "won't drastically change," Kelly said.

From the day Kelly was introduced as Eagles coach, he said a team needs two quarterbacks. Both Foles and Michael Vick started for him last season. When Vick sought a starting job during the offseason, the Eagles were determined to add a quarterback to compete with Matt Barkley for the No. 2 job.

"We always wanted to have three quarterbacks," Kelly said. "We have confidence in Matt, but we didn't want to go in with just Nick and Matt. We needed to have competition at the position, so that's why we brought Mark in."

Kelly said Sanchez is further along than when Foles replaced Vick last season because of Sanchez's experience in different schemes. Sanchez is one of the NFL's most experienced backup quarterbacks, but at age 27 he still has prime years ahead of him.

If Sanchez is injured in Foles' absence, Barkley is the only other healthy quarterback on the roster. The Eagles have G.J. Kinne on the practice squad. Their emergency quarterback for games is either Brad Smith or James Casey, depending on their health.

The rash of injuries this season has shown that the depth chart can be exhausted, but the Eagles hope that Sanchez can stay healthy and thrive. He has a one-year contract, so Sanchez's long-term future is unknown. It depends on how he leads the Eagles during the next two months.

"I think he's fully invested in the team and winning," Kelly said. "It's not about individual accolades. I think he truly understands what we're trying to get accomplished here and was great in terms of assisting Nick in all these games up to it. And when it was his chance to go into the game and play, he did an outstanding job with it."

Jeff McLane contributed to this article.

zberman@phillynews.com

@ZBerm