GREELEY, Colo. (AP) The Denver Broncos received good news when results from an MRI exam showed no structural damage to Terrell Davis' swollen left knee.

Still, Davis' latest setback had the Broncos wondering how much longer their injury-plagued star running back will be able to play.

"I don't think anybody knows the answer to the questions: How much will he play? How long can he play? Will he hold up?" Broncos coach Mike Shanahan said. "We'll just have to wait and see."

Davis received a cortisone shot for swelling and another injection to relieve an arthritic condition Monday, but no one is sure if the treatment will work or when he'll be able to return.

"I was hoping it could have been a better situation if they had seen something and said this is it," Davis said. "There are a lot of different variables now. It is obviously not clear. We will see and go from there."

Davis was arguably the best running back in the 1990s, rushing for 6,413 yards in his first four seasons - the second-highest total in league history. In 1998, he rushed for 2,008 yards and became the eighth player to be named MVP of the league and the Super Bowl during his career.

Then the injuries hit.

Davis tore the anterior cruciate ligament in his right knee in the fourth game of the 1999 season, then played just five games the following year due to lower leg injuries. Last year, he was limited to eight games due a knee injury.

Davis had surgery on his left knee for the second time in a year in May, but was back on the field for a minicamp just three weeks later. The Broncos held him to one practice per day through the first two weeks of training camp and he seemed to be running without pain.

But as he warmed up for Denver's preseason opener against Chicago on Saturday, Davis starting having pain and swelling in his left knee. He told the coaching staff just before the game that he wouldn't be able to play.

"The knee felt like someone had a staple gun and shot it into the side of my knee," Davis said. "The pain was associated with weakness. I couldn't have played in the biggest day of my life."

Davis' latest setback clouds his future, but the Broncos at least have other options.

Olandis Gary, who set a Broncos rookie rushing record two years ago, seems to be back at full strength after tearing his ACL last year, and rookie Clinton Portis has caught the attention of the Broncos coaches with his speed and elusiveness.

The Broncos also have Mike Anderson, the 2000 Offensive Rookie of the Year who switched to fullback this year.

Shanahan said Davis will play Monday night against San Francisco if his knee improves enough, but he plans to give Gary and Portis the majority of snaps during practice this week.

"He doesn't really have to do a lot in practice because we're not going to give him those reps anyhow, and we don't want to take away from the guys we know are going to play," Shanahan said.

"The question is can he get enough work in the scout team where he feels comfortable that he can go into a game and be in football shape and also have enough carries where after the game he feels like he can go the following week? We'll find that out here in the next few weeks."

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