INDIANAPOLIS -- The unthinkable suddenly seems possible in Indianapolis -- opening the season without Peyton Manning.

The four-time league-MVP who has never missed a start in his NFL career is doubtful for Sunday's game at Houston because of lingering soreness in his back following offseason neck surgery. If Manning sits, it would be the first time the NFL's active iron man missed a meaningful game after 227 consecutive starts including the playoffs.

Manning's triceps strength has plateaued and he doesn't have the arm strength right now, sources told ESPN senior NFL analyst Chris Mortensen. Manning also had some back soreness that worsened during the weekend.

The Colts currently have no plans to attempt another surgery on Manning's neck, a source told ESPN NFL Insider Adam Schefter.

"I hate it for Peyton," said Pro Bowl center Jeff Saturday, one of Manning's closest friends. "You want him to be healthy, you want him to be back, but you want him to take care of it, too. It's sad when players face tough times, but I know he's strong enough to get through it."

The question is whether the Colts can survive without their franchise quarterback, whose streak stands second in NFL history to Brett Favre's among all QBs.

His 208 consecutive regular-season starts are the most among active players. If Manning can't start Sunday, Tampa Bay Buccaneers cornerback Ronde Barber, who has started 179 straight games, would take over the top spot if he starts Sunday against the Detroit Lions.

Manning has been the Colts' only starting quarterback for the last 13 years. Over that span, the Chicago Bears have started 17 different quarterbacks, the most of any NFL team. Every team other than the Colts has had at least three different starting quarterbacks during that span.