SAN FRANCISCO -- Just over three hours before first pitch on Saturday, Padres left-hander Clayton Richard was scratched from his start due to flu-like symptoms.

Andrew Cashner, who has been used in long relief this season, got the start against the Giants at AT&T Park.

"He felt queasy last night and was vomiting this morning," said Padres manager Bud Black of Richard, who is one of a handful of players who have suffered a similar malady recently. "He's got a virus. His strength is sapped."

Though he started the season in the bullpen, the Padres envision Cashner as a starting pitcher. He had a 3.86 ERA in five appearances thus far, striking out nine in 9 1/3 innings.

He last appeared in a game was on April 16, when he threw 38 pitches in 1 1/3 innings against the Dodgers.

"There's no hard-and-fast number," Black said when asked how many pitches Cashner was capable of throwing, though the club targeted around 60.

Richard is 0-1 with a 5.28 ERA in three starts. His last start was the best of the bunch, as he tossed six scoreless innings in a no-decision against the Rockies on April 14.

Richard didn't miss a start last season, making 33 en route to winning 14 games. He also made 33 starts during the 2010 season, when he also won 14 games.

Black is hopeful that Richard will be able to pitch Tuesday in the spot that was left vacant when right-hander Tyson Ross went on the disabled list Saturday with a subluxation of the left shoulder.

Cashner made five starts for the Padres last season. He would have contended for a spot in the starting rotation but suffered a lacerated tendon in his right thumb while dressing meat after his hunting excursion with a friend. He came along fast in the Spring Training and landed a bullpen job.

There figured to come a time this season when the Padres would send Cashner to the Minor Leagues to build his endurance and arm strength for a move into the rotation. Could Cashner, if he pitches well Saturday, possibly get another start and keep a spot in the rotation?

"This is an opportunity to give him a start. ... We're sort of adjusting on the fly," Black said. "In April, it's too early to say if he's going into the rotation or not."