INDIANAPOLIS (AP) Robert Mathis returned to the Indianapolis Colts practice field on Tuesday after spending all of training camp on the physically unable to perform list as he continued to rehab from a torn Achilles tendon suffered last year.

His return comes just as Indy is trying to find answers for its struggling defense - specifically when it comes to tackling.

''We had a conversation with our doctors (Monday),'' Colts coach Chuck Pagano said. ''Everybody felt like it was time to put him back out on the grass and ease him back in.''

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The 34-year old linebacker was injured in September 2014 while serving a four-game suspension for violating the NFL's ban on performance-enhancing substances.

Pagano gave no indication when the six-time Pro Bowler would return to the lineup, but Mathis said he will be ready in time for Indy's season-opener on Sept. 13 in Buffalo.

''The toughest part has been just waiting,'' Mathis said. ''I'm just going to be smart about it and just do everything I can to be ready.''

The Colts are ready, too. Indy dropped its first two preseason games to Philadelphia and Chicago, and need help defensively.

The amount of missed tackles in Saturday's 23-11 loss to the Bears threw up a red flag for Pagano.

''We had 13 or 14 (missed tackles),'' Pagano said. ''Certainly not good enough. It's really hard when you don't tackle to the ground during training camp. And you don't do anything during the offseason because you're in shorts.''

That can end up being seven months or more that players don't make an actual tackle. So the Colts are simply trying to get back into a groove. Against Chicago, Indianapolis showed signs of improvement.

In the first half, Indy's starters held the Bears to 0-5 on third down. Twice Chicago got inside the 20-yard line, but didn't score. And the Bears were held to three field goals before scoring twice in the second half to take the lead for good.

Colts linebacker D'Qwell Jackson said better tackling will come with repetition and some focus on the little details of making a tackle.

''The more we get into more of a game mode and start playing games,'' he said. ''It's just a matter of practicing a little bit better when it comes to fundamentals. It's an emphasis on practice and applying it to the game.''

Jackson said he expects to see major improvements when the Colts are at St. Louis on Saturday.

Mathis will provide a boost, too, and already did during his first practice back since missing all of last season.

''Watching him play is a thing of beauty,'' quarterback Andrew Luck said. ''I'm glad he's back on the field. It lifts your spirits.''