Tony Romo is expected to miss the rest of the season after another left clavicle injury. Getty

Once considered one of the top NFC contenders to reach the Super Bowl, the Dallas Cowboys (3-8) appear doomed to miss the playoffs with star quarterback Tony Romo expected to miss the rest of the season after re-injurying his left clavicle in a Thanksgiving loss to the Carolina Panthers at AT&T Stadium in Arlington, Texas.

A source close to Romo told ESPN's Ed Werder that Romo is out for the season, though an official word has yet to be announced. Romo left the game for X-rays after being sacked by Carolina's Thomas Davis, and was later seen in a sling. Matt Cassel played the entire fourth quarter in Romo's place.

Romo, who throws with his right arm, suffered a broken left clavicle in Week 2 against the Philadelphia Eagles and would go to miss seven games, which all resulted in losses. Five of the losses were by seven points or less, as Brandon Weeden and Cassel struggled to keep the offense competitive.

On Thursday, it was Romo who provided little confidence is his ability to run the offense. He threw three total interceptions including two pick 6s, as the Panthers cruised to a 33-14 victory.

Romo's latest injury has fueled speculation that the Cowboys had rushed him back to the field, but head coach Jason Garrett was quick to dispel that notion.

"Whether you like it not, when you don't play for eight weeks it's tough to come back and be the guy you want to be," said Cowboys Vice President Stephen Jones.

In the long term, Romo, who is signed through 2019, should be back at full strength next season, with the injury affecting his non-throwing arm. Meanwhile, the Cowboys are expected to have a high pick in the upcoming NFL draft.