ENGLEWOOD, Colo. – A doctor will quickly tell you everyone heals and recovers differently.

And when it comes to how a player will, or won’t, recover from an injury opinions vary. The Denver Broncos have added three players to their roster over a four-day span where the medical opinions played an enormous role in the decision.

The Broncos used the third day of the draft to add two players -- Michigan tight end Jake Butt and Mississippi quarterback Chad Kelly -- who carry significant injury questions. And Tuesday, the Broncos signed Jamaal Charles, a four-time Pro Bowl selection headed toward his 31st birthday, who has suffered torn ACLs in each knee in his career.

At the center of those decisions is a guy who now sports an artificial knee and may need another in the years to come after a 16-year NFL career filled with aches and pain -- executive vice president of football operations/general manager John Elway -- and the team’s director of sports medicine Steve Antonopulos. Antonopulos is known around the Broncos as “Greek" and has been with the team for four decades.

“I’ve got a tremendous amount of respect for Greek, especially with him working on me for 16 years," Elway said. “He knows me inside and out, so what he tells me, I believe."

Antonopulos’ opinions include those on a long list of surgeons, orthopedists, neurologists -- specialists of every kind that the Broncos have at their disposal. And Elway ultimately looks at all of the information and makes the call.

However, there is little question Charles, Butt and Kelly are on the Broncos’ roster because the proverbial green light came after the medical exams.

Butt could have been a late first-round or early second-round pick had he not torn his ACL in the Capital One Orange Bowl in January. The Broncos selected Butt in the fifth round, and he hopes to be ready to play by the start of the regular season.

“In terms of the injury, I’m right on schedule," Butt said this past weekend. “The plan right now is to be ready for the beginning of the season. I don’t see why that’s not possible, so I can’t wait to get out there in Denver and start working."

Asked when they think Butt will be ready to play, Elway said with a smile “"We thought May. No, I'm joking. We're thinking August -- September is what we kind of thought. ... We know that it's going to take him some time, so we're going to make sure we get him healthy and he's right before we push him into anything."

Kelly, who carried plenty of off-the-field questions into the draft as well for some incidents including a brawl at his brother’s high school football game, suffered a torn ACL last season. He also left his pro day workout with what was described as a wrist injury, but Elway called it a thumb injury this past weekend.

The Broncos decided risk and potential value intersected at the last pick of the draft as they selected Kelly in the seventh round, 253rd overall.

“Well, he's got the thumb, so we think it's going to be August," Elway said. “He's an August-September guy, too, so we realize it's going to take him some time to get healthy."

And in Charles’ case, it was simply a yes-no decision. Charles is 30, he played in just three games in 2016 as he had arthroscopic surgery on both knees before he went to injured reserve. He also suffered ACL tears in 2011 (left) and 2015 (right).

But the Broncos still believe they have a need for some big-play pop in a running game that finished near the bottom of the league’s rankings last season. They brought Charles in for a visit Tuesday and were prepared to sign if they got the thumbs up from the medical staff.

A few hours later Charles had signed a one-year deal that included several bonuses and could be worth $3.75 million if he hits the benchmarks.

“I just wasn’t ready last year," Charles said. “I just went in there and got it cleaned up on my meniscus. That’s what it was. I wasn’t ready last year."

“When you look at it, we got Butt and Chad, if they’re hurt and you think they’re good players, and Jake is not even close to the fifth round if he’s not hurt, sometimes that’s where you can get good value," Elway said. “If you’re willing to be patient with them and give them time to get healthy, then you’ve got a darn good football player. If you can think a little bit on to the future instead just right about now, then you have a chance to pick a player like Jake Butt in the fifth round ... so to get that value, we have to be patient, too."