"As a player in position to land a monster contract extension, tight end Vernon Davis could have sought leverage by skipping the 49ers' voluntary workouts in Santa Clara this week.

Instead, Davis made catches all over the field on Monday as the 49ers' four-day organized team activities began.

"I'm here because this is what I do," Davis said. "I like to work."

A handful of veteran players did skip, although coach Mike Singletary played down the absences. Among the players choosing to stay away were starting cornerbacks Shawntae Spencer and Nate Clements, as well as linebacker Manny Lawson.

Singletary said he recently spoke with Spencer and Clements, and gave them the green light to continue their private workouts. But Singletary said he has yet to speak with Lawson, who, like Davis, is entering the final season of his rookie contract. It is unclear why Lawson is absent, but Singletary was unfazed.

"(Lawson) is a guy I'm not concerned about. He's a bright guy," the coach said. "He knows the plays. He'll be here when he has to be here."

The 49ers' first mandatory minicamp is scheduled for June 17-19. Until then, Spencer is working out in Pittsburgh while Clements is conditioning in Arizona. Neither starting corner has participated in any of the 49ers' voluntary sessions this offseason.

Singletary said he would rather have them in camp but understood their decision."