Kerry Collins, a 16-year veteran, has been brought on standby, but the Indianapolis Colts have dismissed rumours over a possible second surgery on quarterback's neck.
Peyton Manning a doubt for opener
Peyton Manning's consecutive games streak could be history by Sunday.
Team officials said yesterday that the quarterback has been told by doctors not to practise and he will be listed as doubtful for the season-opener against Houston. He is still undergoing tests, but no additional surgery has been scheduled.
"As a result of the most recent development the doctors have decided that Peyton will not practise," a Colts statement said.
"His participation therefore, in Sunday's game versus Houston will likely be doubtful. We will update his playing status as required by NFL policy as the week goes on."
Manning started training camp on the physically unable to perform list as he rehabilitated from neck surgery performed in May.
He was not activated until last Monday, when he returned to practice, albeit with limited work.
When Manning experienced soreness in his back, team officials originally thought it was simply part of the normal rehab process. But over the weekend, the statement said, doctors re-evaluated Manning and told him to stop working out.
"As of now, Peyton continues to deal with a complicated neurological recovery, the end date of which is unpredictable," the statement read.
Manning, the only four-time MVP in league history, has never missed a regular-season start and his streak of 227 games including play-offs is second for quarterbacks; only Brett Favre made more consecutive starts.
If Manning cannot start, the job will likely fall to Kerry Collins.
The Colts brought Collins, a 16-year veteran, out of retirement on August 17 after Jim Irsay, the team owner, told fans to be prepared for the possibility of starting the season without Manning - an unthinkable thought until now.
Speculation about Manning's status began on Sunday night when a local sports talk radio host tweeted that Manning would need a second surgery on his injured neck.
However, Robert Irsay, Jim's father, responded with a tweet of his own, saying there was no change in Manning's status.