Manning's latest neck procedure reportedly was his fourth

As uncertainty over Peyton Manning's health and future in Indianapolis continues to make headlines, more details about the neck issues that forced him to miss the 2011 season have emerged.

SI.com reported Wednesday, citing NFL sources, that Manning underwent a fourth and unreported procedure during the last two years. It has been widely reported that Manning had three such procedures.

According to the report, the unreported procedure took place at some point after a May 23 surgery to correct a bulging disk, but before a cervical neck fusion surgery Sept. 9. The surgeon who operated on Manning in May also did a follow-up procedure in Chicago, according to the report.

Clouding the circumstances surrounding Manning's procedures, and what was reported, is the fact that two of the surgeries occurred during the NFL lockout when teams had limited contact with players.

League sources also told Sports Illustrated that Manning has potentially developed bone spurs in his neck from the fusion surgery that took place in September. The Colts are under the belief that it is almost inevitable Manning will require further surgery at some point, possibly another fusion procedure, according to the report.

The September surgery was intended to repair a damaged nerve in Manning's neck that caused weakness in his throwing arm.

Said Manning's agent, Tom Condon, when asked for comment: "I wouldn't have anything to say about all of that, one way or another."

It's believed Manning began the throwing phase of his rehabilitation process during early December, and doctors "medically cleared" the four-time NFL MVP to play in early February. Reports also surfaced that while the vertebrae in Manning's neck have healed as expected, he continues to experience issues with the nerve regeneration in his arm, affecting his ability to throw.

Colts owner Jim Irsay said Tuesday the team would welcome Manning back but only on a restructured contract that reflects the uncertainty of the quarterback's recovery.

Manning, meanwhile, has maintained during the last several weeks that his recovery process is on schedule.