Wade Phillips, the veteran coach who has turned the Houston defence into the NFL’s best, is taking medical leave to have surgery to address a kidney condition this week.

The Texans said Wednesday that the 64-year-old Phillips is expected to return this season, which will include the expansion team’s first playoff game. But his leave is just the latest roadblock for the Texans, who’ve continued to win despite losing a key player to an injury every week.

Linebackers coach Reggie Herring will run the defence for Houston (10-3) in Sunday’s game against Carolina (4-9). Herring was Phillips’ linebackers coach in Dallas from 2008-10, then joined Houston’s staff after Phillips was hired on Jan. 5.

Phillips was expected to speak to reporters after Wednesday’s practice.

Outside linebacker Mario Williams (torn chest muscle) and quarterbacks Matt Schaub (right foot injury) and Matt Leinart (broken left collarbone) are all out for the season, and star receiver Andre Johnson has a strained left hamstring after missing six games with an injury to his right hamstring. On Monday, coach Gary Kubiak said starting right guard Mike Brisiel had surgery on his broken right leg.

But Phillips has probably contributed more to the Texans’ success this season than anyone.

Fired as the coach of the Dallas Cowboys in the middle of last season, Phillips has talked about feeling rejuvenated with the Texans. He took over the league’s worst 2010 defence and implemented a 3-4 alignment before the season.

Houston leads the league in total defense at 275 yards per game. The Texans rank fourth in rushing defense at 91.5 yards per game and third in pass defense at 183.5 yards per game, and have held each of their last seven opponents below 20 points.

The players credit Phillips with not only restoring confidence to the defence, but also creating a scheme that is fun to play.

“We’re playing good defence all over,” two-time Pro Bowl linebacker DeMeco Ryans said recently. “Of course it feels good, to be able to get out there and stop some people. You’re definitely not worried about people scoring on you because you know everybody is being accountable. Everybody’s holding up their end and knowing what they’re supposed to do, so you’re comfortable when you’re out there.”

Under Phillips’ guidance, several Texans are having career years.

Linebacker Brian Cushing has regained his form from 2009, when he was named the Associated Press Defensive Rookie of the Year. He leads the Texans with 86 tackles, and also has two interceptions and three sacks.

Outside linebacker Connor Barwin leads the team with 9 ½ sacks after moving into Williams’ role, and the same position where DeMarcus Ware excelled under Phillips in Dallas. Barwin, a converted defensive end, has 25 quarterback hits and seven pass break-ups. He had a franchise-record four sacks in Houston’s 20-13 win at Jacksonville on Nov. 27.

Rookie defensive end J.J. Watt has 4 ½ sacks and two fumble recoveries and leads the defensive line with 43 tackles, and rookie linebacker Brooks Reed, pressed into action after Williams was hurt, has already set a franchise record for a first-year player with six sacks.

Phillips has clearly found a new home in Houston under coach Gary Kubiak. He ran the defense in Denver from 1989-92, overlapping Kubiak’s playing career as John Elway’s backup for the Broncos, but their history goes back even further.

Phillips and Kubiak first met in the late 1970s, when Kubiak was a ball boy and Wade was an assistant for the Houston Oilers, who were coached by Wade’s father, Bum.