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The Indianapolis Colts' already beleaguered defense took another hit Tuesday.

Team officials announced that safety Melvin Bullitt, Bob Sanders' replacement, will miss the rest of the season with a right shoulder injury. It's not what the Colts needed after giving up 31 points and 174 yards rushing at Jacksonville.

But it is life in the NFL.

"There's obviously, a lot of work to do on that side of the ball and we've got to get that straightened away," Colts President Bill Polian said on his weekly radio show Monday night. "We've got good players there, but they're not playing well right now."

And now the Colts (2-2) will be short-handed, too.

Bullitt's injury status was first reported by ESPN.com. Players and coaches were not available for comment Tuesday, their regular day off.

He is scheduled to have surgery on the injured shoulder and will be placed on injured reserve.

The former undrafted free agent had started 24 of Indy's past 36 regular-season games, mostly in place of the oft-injured Sanders, and had become one of Indy's most consistent tacklers. So when Sanders went down in the season opener with a torn biceps muscle in his right arm, most figured the Colts' wouldn't lose much by putting Bullitt in the lineup.

He was seventh on the team this season with 13 tackles and had one of the Colts' three interceptions.

Now, with Bullitt out for the season and Sanders expected to miss at least two more months, the Colts' already-thin secondary is in dire need of help.

Veteran Jamie Silva, normally the next in line, went down with a season-ending torn ACL during the preseason, and the Colts started the season with only three safeties on the roster — Sanders, Bullitt and two-time Pro Bowler Antoine Bethea.

Now they only have one of those three — Bethea — available.

Bullitt hurt his shoulder twice Sunday, the second time coming midway through the third quarter. He had already put a hefty brace on the shoulder after getting injured in the first half, the same brace he wore most of last season.

When Bullitt left, recently signed DaJuan Morgan took his place.

Morgan has solid credentials, a third-round pick by Kansas City in 2008 who was signed Sept. 15. This weekend, the former Chief will likely get a chance to start against his former team as the NFL's last unbeaten team visits Lucas Oil Stadium.

Indy also activated undrafted rookie Mike Newton, a safety, from the practice squad and re-signed veteran safety Aaron Francisco, who played with the AFC champion Colts last season after spending 2008 with the NFC champion Cardinals.

The rash of injuries has hit the Indy defense hard.

Besides Sanders and Bullitt, starting linebacker Clint Session missed two games with a hamstring injury before he returned against the Jaguars. His backup, Kavell Conner, had surgery to repair a fractured left foot last week and has already been ruled out of this week's game. Another backup linebacker, Ramon Humber, was put on the waived-injured list after fracturing his right hand two weeks ago, and the Colts lost six defensive backs to season-ending injuries during training camp.

Plus, they have to fix a defense that has struggled to pressure quarterbacks the past two weeks and is allowing nearly 150 yards per game, 29th in the NFL.

"The way to develop consistency, and I'm going to paraphrase the great John Wooden here, but the best way to help the team is to improve yourself," Polian said. "So everybody on the team has to do the best they can do. If everybody concentrates the best they can do, if everybody goes out and does the best they can every week, things will work out."

But it's not just the defense taking hits.

Receiver Anthony Gonzalez is set to miss his fourth straight game this weekend against the Chiefs, and rookie kick returner Devin Moore will be placed on injured reserve with nerve damage in the neck or shoulder area.

Indy also released defensive tackle Mitch King from the active roster and receiver Alric Arnett from the practice squad, and signed receiver Kenneth Moore.