Opportunities for undrafted free agents can prove fleeting. One moment they have a chance to show what they can do, and the next they're handed an airline ticket home.

The Bears saw enough promise to keep Roy Robertson-Harris around all last season, even though a serious heat-related illness he suffered in July before reporting to training camp wound up sidelining him for the entire season.

Now Robertson-Harris is trying to adjust to a new position. He moved from outside linebacker to defensive end in December, when all he could do was work out in the weight room and attend meetings.

The former UTEP Miner came in at 6-foot-7, 265 pounds last year, and a season spent lifting weights has filled out his frame to a rock-solid 285, too big to be an outside linebacker. He played on the line in college, so it's not a completely new position with OTAs underway and minicamp a little more than two weeks away.

The good news for Robertson-Harris is the Bears didn't draft a defensive lineman, but they did sign free agents Jaye Howard and John Jenkins and hope 2016 third-round pick Jonathan Bullard, a disappointment last year, takes a major step forward.

"This isn't anything I haven't done before," Robertson-Harris said of the position switch. "It's just going against stronger guys."

Robertson-Harris was working out in Houston before camp last summer when he became ill. He was sidelined to begin camp, and after he played 14 snaps against the Chiefs and 12 against the Patriots in the first two exhibition games, the Bears learned he wasn't fully recovered and placed him on the non-football illness reserve list.

His body rebounded and he has learned how to hydrate better. How will he avoid a similar incident?

"Don't train in Houston in July," he said. "I am not worried about it. I know what to do to take care of my body now. The worst with that is all done. Just moving forward and putting the right things in my body and making sure I am good."

Tribune Bears reporters Dan Wiederer and Rich Campbell discuss the team's quarterback situation. 

Tribune Bears reporters Dan Wiederer and Rich Campbell discuss the team's quarterback situation. 

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He returned to the Chicago area in March to begin training before the voluntary offseason program started and will remain here in June and July to avoid the heat and humidity in Texas. Robertson-Harris needs to open eyes when the pads go on in camp to work his way up the depth chart.

"We got that (illness) under wraps," coach John Fox said. "He's gained a lot of bulk and strength. I like what I've seen from him thus far, both in offseason conditioning as well as the immediate practice work."

Robertson-Harris, who earned $333,000 last season, flashed in his brief preseason action. He was lined up in the slot when he blew up Chiefs wide receiver Demarcus Robinson, who was attempting to block, and tackled wide receiver Da'Ron Brown for a 3-yard loss on a bubble screen. He also knocked down Chiefs quarterback Aaron Murray on a pass rush.

"It's the highlight of my career basically," he said. "Those plays I like to look back on, and, yeah, I got a chance to play, but I am trying to look past preseason. My main goal is to make the 53(-man roster) and stay all year."

Last summer the Bears were teaching Robertson-Harris to play in space, something he had not done before. He's more comfortable with his hand in the dirt but will have to prove he can be effective and play with leverage against NFL talent.

He needs to use his hands and feet properly. He has plenty of raw athletic ability, but it won't serve him well without the technique. With his length, he wants to watch tape of similarly built players such as Calais Campbell, Michael Strahan and Justin Tuck.

He has gone from sitting in the back of the meeting room and taking it all in to getting reps on the field for a team that needs young, reliable players to emerge on both sides of the ball.

"I like to think (general manager) Ryan Pace has faith in me, and I definitely appreciate him keeping me around when I dealt with what I did last year," Robertson-Harris said. "I am just trying to put in everything I can to prove him right."

bmbiggs@chicagotribune.com

Twitter @BradBiggs

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