ARLINGTON, Texas -- Dallas Cowboys quarterback Tony Romo underwent tests Tuesday morning for a more complete look at the bruised back he suffered in the third quarter of Monday's 20-17 overtime loss to the Washington Redskins.

X-rays at the game were negative, and Romo was able to return in the fourth quarter after taking a painkilling shot.

"We'll get the tests today, but we anticipate him being ready to go [Sunday against the Arizona Cardinals]," coach Jason Garrett said on 105.3 The Fan in Dallas Tuesday morning. "When we left the stadium last night, he seemed like he was OK, and we'll get the tests today to verify everything."

Garrett said Tuesday afternoon, however, that the team was still awaiting the results of the CT-scan on Romo's back.

On Monday, Romo spoke optimistically about being able to play Sunday.

"It's just hard when you lose," Romo said. "Obviously it's the worst thing you feel like you go through. We're disappointed about this game but we're going to have to figure it out within 24 hours and move past it and move on to the next game. Obviously with the injury aspect of it, you feel like you may have dodged one from that regard. That's why you do all the things you do to hopefully withstand stuff like that."

Romo took a knee from Redskins linebacker Keenan Robinson to his surgically repaired back with 7:50 to play in the third quarter. He remained on the field for a few minutes before slowly walking off with the medical staff around him.

Brandon Weeden filled in for two series, directing the Cowboys to 10 points, but Romo was able to return and had a chance to win the game in the final minutes of regulation. In overtime, his fourth-down pass to Dez Bryant was knocked away by Bashaud Breeland to end the game.

Romo often has said that if he can return to action after suffering an injury, he should be able to continue to play. Last December against the Redskins, Romo aggravated his back but played through it and threw a fourth-down touchdown pass to DeMarco Murray to win the game.

Five days later, he needed surgery to repair a herniated disk.

Garrett said there were no second thoughts about putting Romo back in the game.

"Obviously Tony's our quarterback," Garrett said, "so if Tony's healthy and ready to go, he's going to play."

Tony Romo lays on the ground after being sacked by Keenan Robinson during the second half Monday. AP Photo/Tim Sharp

Romo finished the game with 209 yards on 17-of-28 passing. He threw a second-quarter touchdown pass to Bryant but was sacked a season-high five times. He lost one fumble that Murray recovered on the final drive.

After a sluggish start to the season, Romo and the medical staff altered the quarterback's practice schedule. Romo has not practiced on Wednesday the past six weeks as he has continued to strengthen his back.

The time off has helped Romo on game days. Before last week's game against the New York Giants, Romo took a Toradol shot to soothe his sore ankle and ribs, and he completed 17 of 23 passes for 279 yards and three touchdown passes.

Romo wasn't sure how much he would be able to practice this week.

"I'm just trying to figure out how to get through tonight and tomorrow," Romo said. "We'll figure out a way to adjust and move on through the week. We've got to get ready for Arizona, and it is going to come up fast."

Cowboys owner and general manager Jerry Jones said after the game that Cowboys linebacker Justin Durant suffered a torn right biceps during the game and is out for the season.

"It hasn't sunk in yet," said Durant, who had stepped up as a leader for the defense.

The loss of Durant, a captain, is a major blow to a defense that has far exceeded expectations after allowing the most yards in the league last season.

"He's in the top three or four performers we've had this year on defense," Jones said. "He plays a key position, that weakside linebacker principally. That's a significant loss for us."

Durant leads the Cowboys in tackles (51 entering Monday night, according to the coaches' count from film study) and forced fumbles (two) this season.

"It's a big loss for us," cornerback Brandon Carr said. "That was our guy that held down the middle for us, called all the plays, made a lot of plays for us in a short amount of time this season. We're definitely going to miss him, but he's going to be around. Now it comes to the next-man-up mentality."

Left guard Ronald Leary suffered a strained groin and did not play in overtime. Leary said he would undergo an MRI on Tuesday to determine the severity of the strain but hoped to be able to play Sunday against Arizona.

ESPNDallas.com's Calvin Watkins and Tim MacMahon and The Associated Press contributed to this report.