Source: Peyton Manning throws at Duke

Indianapolis quarterback Peyton Manning took another positive step forward in his recovery from neck surgery on Friday, conducting an aggressive throwing session in his Colts helmet, shoulder pads and jersey at Duke University, a source in attendance told ESPN.

Manning can be seen in a video clip posted late Friday on YouTube, independently verified as authentic, making apparent encouraging progress in his recovery from the surgery that sidelined him for all of last season. The session comes as a Thursday deadline approaches for the Colts' decision to exercise their $28 million option on Manning.

Manning can be seen completing passes in the video posted by a user who had access to a videotaped portion of the session near the Duke practice field.

Sources at Duke and close to Manning confirm he has been conducting aggressive throwing sessions in shoulder pads and helmet since Tuesday at Duke, where his former University of Tennessee offensive coordinator David Cutcliffe is now the head coach. It is Manning's second trip to work under the supervision of Cutcliffe.

Among those who have joined Manning in Durham, N.C., include Colts teammates Dallas Clark and Austin Collie, as well as former teammate Brandon Stokley, sources said.

Manning was spotted at a local Durham restaurant Friday evening signing autographs during dinner, a source said.

Manning has increased his throwing regimen as Colts owner Jim Irsay contemplates a decision on whether to exercise the option. Manning and Irsay also have had conversations about the veteran quarterback continuing his career as a Colt, even though it is likely the team is set to use the No. 1 overall draft pick on former Stanford quarterback Andrew Luck or former Baylor quarterback Robert Griffin III in April.

Several sources have told ESPN during the past month that Manning's throwing strength has dramatically improved as his nerves continue to regenerate following his latest neck surgery Sept. 8. Dr. Robert Watkins, who performed the single-level cervical fusion, has stated publicly that he has cleared Manning to resume his playing career.

Irsay has stated Manning still needs to pass a team physical even though sources have said that Colts neurosurgeon Dr. Hank Feuer has also told Manning it would be safe to resume his career.

Chris Mortensen is ESPN's senior NFL analyst.