BOURBONNAIS, Ill. -- The season-ending foot injury suffered by Chicago Bears tight end Zach Miller against the Jacksonville Jaguars on Thursday proved to be another in a string of health-related disappointments dotting his career.

The injury carrying more significance to the team at this point, however, is the ankle injury suffered by rookie cornerback Kyle Fuller. It's an injury that can impact two positions in a secondary already in question because of the team's problems at safety.

Fuller had been playing with starters at left cornerback in the nickel defense and Tim Jennings moved from starting left corner to nickel back. So losing Fuller for any length of time not only deprives the rookie of valuable developmental time, but Jennings will be doing double duty while still trying to learn a new spot on the interior of the defense.

Coach Marc Trestman sees Jennings as capable of doing both jobs, and saw him as an ideal candidate to play nickel even if he lacks experience there.

"I mean his leverage, his understanding of how to play inside was excellent through the camp and the time that he played," Trestman said.

Jennings, though, has missed more than half of training camp practices with his own injury problem -- a quad strain.

"He was highly competitive covering our receivers inside during camp before he got hurt," Trestman said. "So I think that transition is something that he's going to be able to handle easily."

Fuller is viewed as a rookie capable of handling obstacles like several missed practices, although the Bears hadn't said how serious the ankle sprain was. Fuller was able to walk off to the locker room during the game to have the ankle examined.

"He has a very good mental disposition towards competing at that position," defensive coordinator Mel Tucker said. "He's a guy that doesn't get too high and he doesn't get too low and those are good traits to have at corner."

Miller had a concussion at the end of the 2010 season followed by knee, foot and shoulder injuries in 2011 and a torn pec in 2012. But he had begun to look like an ideal tight end to put on the field with Martellus Bennett when the offense went to a two-tight end set.

Tight end Dante Rosario is more of an H-back type and Miller, who caught six passes for 68 yards and two touchdowns, figured to be more of a tight end in a classical sense.

"You guys saw him out at practice," Trestman told the media. "He had an excellent camp. Things transitioned from the practice field to the games over the last couple weeks. That was clear."

Backup quarterback Jordan Palmer saw Miller's abilities and injuries firsthand in Jacksonville in 2012 and said he tried to get Arizona to sign him when he was playing with the Cardinals. He thinks the Bears haven't seen the last of Miller, though he was placed on season-ending injured reserve.

"It's just a total bad-luck injury," Palmer said. "The way he's handled this in the past, I know he's going to make the most of this. He's going to heal quickly, rehab, do everything they ask him to do. He's going to contribute somewhere. If it's here, hopefully he comes back."

Without the budding third tight end, the Bears' other option appears to be former Jet-Ram-Patriot Matthew Mulligan, who is weighing in close to 280 after playing around 20 pounds lighter earlier in his career. He views himself as more of a blocking tight end but did show an ability to go vertically down the field. His agility in the open field is not close to Miller's though.

"He's shown good hands and good speed, besides his ability to block at his point of attack, so we're excited about it," Trestman said. "He's got great experience. He's been in good programs and he's a good add by (general manager) Phil (Emery) and his personnel department."