Two years ago, it appeared the Indianapolis Colts had the makings of one of the NFL’s outstanding secondaries. Two weeks ago, it appeared it was all about to come together.

Not this year.

Safety Bob Sanders has been placed on injured reserve and will require season-ending surgery to repair a torn biceps, and starting cornerback Kelvin Hayden is expected to miss up to four weeks with a knee injury, the club announced Friday.

With the season-ending knee injury cornerback Marlin Jackson suffered in practice Wednesday, free safety Antoine Bethea will be the only member of the projected starting secondary on the field Sunday when the Houston Texans meet the Colts in a key AFC South game at Lucas Oil Stadium.

“I guess you never know,” Bethea said. “We always talk about it, me and Bob, Marlin, Kelvin. We were always saying if we could get on the field together, maybe it would be something special. But then it was always one guy missing, two guys missing. It’s just tough.”

The Colts also announced that wide receiver Anthony Gonzalez will miss additional time after undergoing arthroscopic surgery on his right knee Thursday. Gonzalez has not played since suffering ligament damage during the season opener.

Free agent defensive end Josh Thomas was signed to fill the roster spot vacated by Jackson, who tore his left anterior cruciate ligament in a non-contact drill. Tight end Tom Santi was signed to fill Sanders’ spot.

It has been a week of big hits for the NFL’s No. 1 scoring defense (13.0 points a game). Strong-side linebacker Tyjuan Hagler was placed on injured reserve Wednesday with a ruptured biceps. Coach Jim Caldwell said Philip Wheeler probably will start there, but the Colts have another option: Freddy Keiaho, a two-year starter on the weak side who has been backing up middle linebacker Gary Brackett.

“He can play all three (linebacker slots). He’s very capable,” Caldwell said.

Sanders and Bethea have been to the Pro Bowl and the Colts annually have been among the league leaders in pass defense, but the backfield they envisioned never has come together. Sanders, Bethea, Jackson and Hayden started 12 games together in 2007, two in 2008 and none this year. Injuries have intervened.

Sanders has missed 40 of 87 games over his 51/2 NFL seasons. The league’s 2007 NFL Defensive Player of the Year missed the first five games of this season while completing rehabilitation from offseason knee surgery. He suffered the left elbow injury Sunday against San Francisco and sought a second opinion Thursday from Dr. James Andrews, a noted orthopedic surgeon in Birmingham, Ala.

With Hayden and Jackson out during Week 5 at Tennessee, rookies Jerraud Powers and Jacob Lacey started. Powers has started six games, Lacey one. Four-year veteran Tim Jennings joined them in the nickel package.

That threesome could be on the field a lot Sunday. Houston lost tight end Owen Daniels last week to a season-ending knee injury and reserve tight end James Casey (knee) also is out. The Texans could go extensively with a three-wide receiver set.

T.J. Rushing, who is primarily a punt returner, is the Colts’ fourth cornerback.

Houston’s third-ranked passing attack features quarterback Matt Schaub, whose 2,342 passing yards and 16 touchdowns are NFL bests, and wide receiver Andre Johnson, who leads the league with 697 receiving yards.

The Colts are 7-0 this year largely because of their “next man up” philosophy and their ability to build a 53-man roster. It will be tested Sunday.

There is a trickle effect when players like Melvin Bullitt (Sanders’ replacement), Lacey, Jennings and Wheeler are forced into larger roles. All are key kick and punt coverage players, and Houston return men Jacoby Jones and Andre Davis are among the league’s best. Jones has a 62-yard punt return and a 95-yard kick return this season.

“You’ve just got to take the same approach,” said Bullitt, a special teams co-captain. “You know it’s going to be a grind, but we’re getting into that time when everybody’s hurting, everybody has somebody on their team with significant hurts.”

Etc.

Linebacker Clint Session was fined $5,000 by the NFL for roughing 49ers quarterback Alex Smith last Sunday, specifically for striking Smith in the knee area. . . . A limited number of tickets for Sunday’s game returned by the Texans remained available late Friday. They are available at the Lucas Oil Stadium ticket office or through Ticketmaster.

Call Star reporter Phil Richards at (317) 444-6408.