OXNARD, Calif. – Jason Witten is going to have to get used to not doing much of anything if he wants to play in the opener next month.

Dallas Cowboys Coach Jason Garrett said Wednesday that his Pro Bowl tight end sustained a “slightly lacerated” spleen in the preseason opener Monday night against Oakland. The best way for Witten to heal is to remain as inactive as possible.

“It’s a very serious injury and we’re really taking this thing day by day,” Garrett said. “He has to be very still and idle for the next week to 10 days, so you won’t see him out here on the practice field. He won’t play in the game this week or next week. We’ve just got to make sure he heals as well as possible, as quickly as possible.”

Witten is expected to miss the rest of the preseason, starting with Saturday night’s game at San Diego. The Cowboys open the season Sept. 5 at the New York Giants.

Garrett said doctors will reassess Witten next week “after we’ve had a few days of him not doing anything.” Surgery would be an option if the spleen isn’t healing properly by then.

The Cowboys’ owner, Jerry Jones, said after practice that he hasn’t even looked at whether Witten would be ready for the opener against the Giants.

“We basically were more interested in (the) rest of this week and getting that healed back up,” Jones said. “It’s diagnosed real good with the cut on his spleen. He can’t do anything or move around too much. And then it heals up like any cut; hopefully he will be back.”

Witten apparently got hurt after he caught a pass from a scrambling Tony Romo and was immediately hit from the side by Oakland linebacker Rolando McClain. The play resulted in a 2-yard loss.

Witten has missed only one game in his nine NFL seasons. That was as a rookie in 2003 when he had a broken jaw.

“Asking Wit to be still and idle is a hard thing; that’s the biggest challenge right now. But he has to do that, he just has to let time heal it,” Garrett said. “Jason has gotten off to a tremendous, tremendous start to training camp and laid a great foundation for himself. He’s looked as good as I’ve seen him look since I’ve been around him.”

Witten is a seven-time Pro Bowl player who is one of Romo’s best friends and one of the quarterback’s favorite targets. The tight end has 696 career receptions, second in team history behind only Hall of Fame receiver Michael Irvin at 750.

Because Witten has started every game the past five seasons, and all 77 games Romo has started since becoming their No. 1 quarterback in 2006, the Cowboys aren’t concerned about him missing some time in training camp.

“I don’t think this, at the end of the day, him being away from our football team and off the practice field, is going to be that detrimental to him. In fact, I think it’s going to allow him to get his legs back a little bit, and be fresh and ready to go,” Garrett said. “We’re going to spin this thing positively and say hey, this rest will help him.”

The Cowboys signed free-agent tight end Harry Flaherty, the nephew of the head coach and tight ends coach John Garrett. He signed with New Orleans as an undrafted rookie out of Princeton last season but was cut early in camp. To make room on the roster for Flaherty, the Cowboys waived injured guard Bill Nagy.

John Phillips, a fourth-year player, likely will fill in as a starter for Witten. Rookie tight end James Hanna also will get more work.

Phillips missed the game against the Raiders because of a sprained ankle but was back at practice. He said the swelling was gone and his ankle was good.

BRONCOS: Defensive end Jason Hunter had surgery on his torn triceps and is out for four months.

Coach John Fox also said right guard Chris Kuper had surgery on his broken left forearm and is out 4 to 6 weeks.

n Jurors convicted linebacker D.J. Williams of driving while ability-impaired. He was also convicted of driving without headlights, the offense that prompted police to stop him about 3 a.m. on Nov. 12, 2010.

TITANS: Tennessee signed offensive linemen Michael Jasper and Jonathan Palmer to boost its roster numbers up to 90 after a couple of injuries.

Center Eugene Amano tore his right triceps early in training camp, left guard Steve Hutchinson has been getting some time off for rest and tackle Mike Otto dislocated his ring finger Tuesday night. Coach Mike Munchak said they wanted some depth.

STEELERS: Linebacker James Harrison underwent left knee surgery, clouding his chances of returning in time for the start of the regular season.

Coach Mike Tomlin called the procedure “minor” but wouldn’t put a timetable on when Harrison will be ready. Harrison will remain on the physically unable to perform list indefinitely.

JETS: Linebacker Bart Scott has high expectations for quarterback Mark Sanchez, saying he wants Sanchez to “take the next step” of becoming one of the top 10 players at his position.

Scott said there’s a noticeable difference in how Sanchez carries himself as a leader this season, the quarterback’s fourth in the NFL. Scott said Sanchez “sticks that chest out like a peacock and I think that really shows confidence.”

Nose tackle Sione Po’uha said he expects he could miss the rest of the preseason with a stiff back but is confident he will play in the Sept. 9 opener against Buffalo.

PANTHERS: Carolina ended training camp at Wofford College with several key positions still up for grabs.

The Panthers left with ongoing competitive battles at the starting cornerback and free safety spots, the No. 3 receiver position and both kicking spots.

BILLS: Backup defensive tackle Kellen Heard returned to practice a day after hurting his lower right leg.

Coach Chan Gailey said tests came back negative and Heard should be ready to play in the Bills’ second preseason game Friday night at Minnesota.

JAGUARS: Jacksonville could be without starting left tackle Eugene Monroe for Friday night’s preseason game at New Orleans.

Monroe left the practice field on a cart after getting hit in the head during drills. Team doctors were checking him for a possible concussion, and Coach Mike Mularkey said the results will determine whether Monroe plays against the Saints.

LIONS: Running back Mikel Leshoure returned to practice after recovering from a right hamstring injury.

Leshoure has missed most of training camp because of the injury, but he was on the field with the team. The Lions could use a healthy Leshoure because running back Jahvid Best is still out with concussion problems.