They could be without middle linebacker Anthony Walker, too.

On Friday, coach Frank Reich ruled out Leonard and left tackle Anthony Castonzo for Sunday's game at Cleveland, and acknowledged Walker's status was still uncertain.

“We’ll see how he responds to the limited work he got today and make that decision tomorrow," Reich said when asked about Walker. “Obviously, if he can go, we’d love for him to be out there. He’s a big part of our defense, a big part of our success and when Darius hasn’t played he’s had huge, huge games. So hopefully he responds well to the work today."

The Colts (3-1) have won three straight since an opening-day loss at Jacksonville, and they've done it largely because of their stingy defense.

Indy has given up the fewest yards per game (236.3), the fewest points per game (14.0) and fewest yards passing per game (159.3) while ranking fourth against the run (77.0).

But the Colts deep linebacking corps has been depleted badly by injuries over the past two weeks.

Leonard missed the second half at Chicago after injuring his groin and didn't practice all week. Walker hurt his ankle in Wednesday's practice, sat out Thursday and did limited work Friday. Indy's other starting linebacker, Bobby Okereke, had thumb surgery Tuesday, sat out Wednesday and returned to the practice field Thursday with a protective wrap around his hand.

Even the backups are struggling to stay healthy. E.J. Speed hurt his elbow against Chicago and did limited work Wednesday while being a full participant the next two days. And Matthew Adams went on injured reserve Sept. 26 with an ankle issue.

When Leonard missed three games last year, Reich adapted by moving Walker to outside linebacker and plugged Okereke in at middle linebacker. It could happen again — if both are cleared to play.

Meanwhile, the loss of Castonzo creates a huge void on an offensive line that has started the same five players in a league-high 20 consecutive games. The timing couldn't be worse.

Indy was hoping Castonzo could neutralize one of league's top pass rushers, Browns defensive end Myles Garrett, on Sunday. Instead, that role will likely be filled by veteran Le'Raven Clark.

And it could force the Colts to make additional changes to the game plan.

“We think he (Castonzo) is a great player. So a lot of times in protection, you don’t have to help him as much," Reich said. “If you want to keep a guy to help in protection, it comes at the cost of not getting a fifth guy out in the pattern.”

But Reich remains confident that Clark can get the job done.

“I’m excited to see Le'Raven play," Reich said. “I thought he had his best training camp since I've been here. He’s looked as good as he’s looked the three years I’ve been here. I think he’s going to come in and play well."

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