LAKE FOREST, Ill. — The Chicago Bears defense has five starters 31 or older, and 34-year-old linebacker Brian Urlacher is coming off knee surgery a month ago.

They believe they have lost very little because of age. They also think anyone who doubts it should test them.

“They can try,” linebacker Lance Briggs said. “But they will fail.”

Urlacher was held out of Thursday’s practice, but the plan is to practice Friday and play Sunday in the opener against the Indianapolis Colts.

“He’s had trouble with his knee so we’re not going to push the knee through the week,” coach Lovie Smith said.

Although Urlacher realizes his surgically repaired left knee will never be the same, he anticipates no diminished returns. The same goes for the “seasoned” Bears defense in general as preparations continued Thursday for Sunday’s game at Soldier Field.

“I’m not up to speed,” Urlacher said. “I know the defense well, but I’ve got to get my technique down and work on some things. I’m practicing, so that’s all that really matters to me.”

The Bears defense will face rookie No. 1 draft pick Andrew Luck and the Colts. However, it may be the Colts testing Urlacher. At 34 and with a banged-up knee, it wouldn’t be a surprise to see the Colts — and other teams later in the season — go at the middle of the Bears cover-2 zone to see if their defensive leader has lost a step.

Another 30-something, defensive end Israel Idonije, doubts Urlacher will be slowed against the rush as well.

“If anyone is thinking that Brian is going to be a weak part of the defense, absolutely, run at him,” Idonije said. “The guy, he’s a physical specimen. He’s worked hard to put himself into a position so he can be on the field, and just he is one of those guys who is relentless. If that’s something they think they can exploit, by all means they’re going to try. Then at the end of the day we’ll see.”

Urlacher said he and the other older players — Briggs, Idonije, cornerback Charles Tillman, and defensive end Julius Peppers — are better in the defense now even if age has taken away some of their speed.

“Whatever we have lost in athletic ability or speed or whatever, I think we make up for it with our mental game just like most players do when they get older,” Urlacher said. “They get smarter as they play longer and hopefully get better as they get older.”

Urlacher practiced only the first four days of training camp before experiencing left knee pain that required an Aug. 14 arthroscopic surgery. As a result, he missed all of the rest of training camp and the preseason, then practiced Monday and Wednesday this week.

“I knew I would get back before the first game,” Urlacher said. “It was a matter of getting to this point. It really wasn’t that frustrating. A little annoying when it happened, but once we did the scope, it was fine.”

Urlacher expects no limitations against the Colts.

“Every other game I have ever played I’ve planned on playing the whole game,” he said. “That’s what I plan on doing right now.”

Urlacher’s preparation might change somewhat prior to the Week 2 game against the Green Bay Packers. It’s a Thursday night game, so his recovery time from the first game would be short.

“I’ll do the same thing I always do,” he said. “Get in the cold tub a lot, ice, everything the trainers tell me to do. Try to keep my legs strong. Nothing more than normal. Probably a lot of rest next week with the short week. I have to get on the practice field eventually, but I think we only have one day of practice next week so I’ll just be out there for that if I can.”

Urlacher originally injured his knee in the 2011 regular-season finale.

Several reports have said he went to Europe and underwent a noninvasive procedure on the knee, then relied on rehab to recover from two sprained ligaments. However, he ran into problems at training camp at Bourbonnais.

“I hadn’t done that much in the offseason,” Urlacher said. “I ran the whole month of June and July before I got to training camp. But nothing like we did in training camp and I think I kind of just aggravated it a little bit and got some things loose in there so we cleaned it out and now it’s good.”