So he ordered wide receiver Brandon Marshall on Friday to practice for the first time since pulling his left quadriceps at a minicamp a month ago.
"I was shocked. I was scared, but I guess that's what it takes," Marshall said. "Coach has like 30 years of experience, this is my second year. So, of course I've got to sit back and listen."
Shanahan insisted that Marshall's leg was healthy and that he just needed to suck it up.
"Right now it's healed," Shanahan said. "When you take a look at the MRI and you take a look at the muscle and they say there is no tear anymore and it looks good, he has to fight through a little pain, a little scar tissue."
Marshall had mixed feelings about being pressured into practicing before he felt he was ready.
"Sometimes you don't have no choice," he said. "If it was up to me, I wouldn't have went. But Coach got me out there. It's feeling good. I was kind of hesitant at first, but you see I've got a smile on my face (now)."
Marshall had to practically be pulled off the field by the end of the morning workout.
"When I first got out there and we were just jogging and running fade routes in the end zone. I'd try to do a route and I felt like, 'Why the heck they got me out here?' But as I went, just listening to Coach, it warmed up perfect," Marshall said.
"I was actually supposed to be done in the first 20 minutes, I was just supposed to do the warmup, but it warmed up so good that I just kept jumping in there," Marshall added.
"They were like, 'Did you just go in there?' and I was like, 'Yeah,' and they'd say, 'Don't go in there no more,' and then I'd go back in there. Finally, Greek (athletic trainer Steve Antonopulos) had to grab me and say, 'Don't go back in there anymore."'
Marshall said his thigh was sore after practice and he figures it'll be that way for another week or so, "But I'll keep pushing myself, keep practicing and being aggressive on it and one day I'm going to wake up and the pain's going to be gone."
Before Friday, about all Shanahan had to say regarding Marshall was that he "looked good on the treadmill." Even that jab didn't spur Marshall to get back onto the field sooner. He said earlier in the week that he was planning on returning to practice when the Broncos hold workouts with the Cowboys in Dallas next week.
Despite missing so much time, Marshall still has a solid shot at winning the starting split end job opposite flanker Javon Walker, in part because other receivers have been hobbled themselves.
Brandon Stokley (thigh), Glenn Martinez (thigh), Marquay McDaniel (hamstring), David Kircus (hamstring) and Domenik Hixon (shoulder) have all joined Marshall and Rod Smith, who is recovering from hip surgery, on the sideline.
Marshall missed most of training camp as a rookie because of a knee injury that stunted his growth in the NFL before he came on strong down the stretch, serving as one of Jay Cutler's favorite targets.
He's got a lot of catching up to do after missing the first 11 days of two-a-day practices.
"How long is it going to take him to get into football shape? Probably the same length of time it took these guys to get ready for the first game -- a couple of weeks," Shanahan said. "But he's in pretty good condition because he's been working out in that weight room and you've got to feel comfortable coming in and out of breaks.
"It's going to hurt for a little bit, but as you saw today he did some good things."
Copyright 2007 by The Associated Press