Webb passed a team physical, sources say, but insurance companies use a higher standard when assessing risk. Multiple companies raised concerns, creating a "red flag" for the Diamondbacks, sources say. The contract was contingent on the club securing an appropriate insurance policy for the pitcher.

The condition of Webb's arm became an issue on Wednesday when the Diamondbacks said that he would miss his next start due to shoulder stiffness. But Webb, who turns 30 on May 9, has been extremely durable for most his career.

Webb's only career trip to the disabled list, for elbow tendinitis, was from May 24 to June 8, 2003. No major-league pitcher threw more innings from 2005 to '08.

All veteran pitchers experience wear and tear on their arms; Webb, despite the insurance companies' concerns, might pitch 10 more seasons without injury, one source said.

He completed last season without disruption, tying for the major-league lead with 22 victories and earning a top-two finish in the National League Cy Young Award voting for the third straight year.

The extent of Webb's shoulder problem, which surfaced in a poor opening-day start against the Rockies, is not yet known.

Diamondbacks manager Bob Melvin told reporters that Webb would not throw for two days so the team's training staff can "just work on him a little bit and try to get whatever is in there out of there." No determination has been made on whether to place Webb on the disabled list.

Meanwhile, the uncertainty over his future lingers.

Webb is under contract for $6.5 million this season. The Diamondbacks hold an $8.5 million option on him for 2010. The proposed extension, which was for $2 million more than the Padres awarded right-handed Jake Peavy in a similar deal, would have tied Webb to the club through '13.

Webb disclosed last August that the team had pulled its offer, but neither the pitcher nor club gave a reason for the failed negotiations.

Diamondbacks general manager Josh Byrnes declined comment Wednesday night when asked why the talks sputtered. Webb's agent, Jonathan Maurer, was not available for comment.