Mario Williams' season-ending injury leaves Texans reeling (Update)

Mario Williams has 53 sacks in 82 career games. (AP)

A report early Monday seconded what SI.com's Peter King reported on Football Night in America Sunday night: The Texans will be without Mario Williams for the season.

Williams apparently suffered a torn pectoral muscle in Sunday's Houston loss to Oakland and will undergo surgery this week, which would force Williams to the injured reserve. Williams came off the field in the first quarter after sacking Oakland QB Jason Campbell. He walked to the locker room under his own power.

The Raiders kicked a field goal three plays later, then went on to score 22 more points against the Williams-less Houston defense.

Despite switching to a 3-4 formation this season, the Texans have thus far been a top-10 defense in points allowed and are fourth in the league with 15 sacks. Five of those belong to Williams, whose pass-rushing ability has been one of the keys to Houston pulling off defensive changes under new coordinator Wade Phillips.

Williams wound up on injured reserve with a groin injury last season after struggling through 13 games. The Texans went 1-2 in his absence.

Big picture, the significant injury to Williams could change the landscape of an already-reeling AFC South. The Colts (0-5) and the Jaguars (1-4) have fallen off the pace to start the season, with Houston and Tennessee tied at 3-2. However, with Peyton Manning on the shelf, this looked like by far the Texans' best opportunity to claim a division title and their first-ever playoff berth.

Houston may still be the team to beat without Williams. But Tennessee, which turned in a lackluster performance at Pittsburgh Sunday, has to be licking its chops.

The two teams meet in Tennessee in two weeks. Before that, Houston has to travel to AFC North-leading Baltimore in Week 6.

Can the Texans end their playoff drought without Williams? Maybe, but the task will be a whole lot tougher.

UPDATE: