SAN DIEGO -- Padres manager Bud Black remained unwilling to divulge the club's pitching plans for Wednesday's game in Arizona.

When the Padres designated right-hander Edinson Volquez for assignment on Saturday, it freed up a spot in their starting rotation.

It appears -- in the short term, at least -- that slot will either be filled by left-hander Robbie Erlin or right-hander Tim Stauffer. Righty Burch Smith would seem to be out of the mix after he pitched five innings for Triple-A Tucson on Saturday.

The 22-year-old Erlin is 8-3 with a 5.07 ERA for Tucson. He has made six appearances for the big league club this season, and is 1-2 with a 7.15 ERA.

The primary reason for the timing of the Volquez move was to allow the club a chance to evaluate some of its young pitching options at the big league level, meaning both Smith and Erlin will likely get a look once rosters expand Sept. 1.

Still, the veteran long-reliever Stauffer remains the only option on the active roster. Black said Stauffer was unavailable for Sunday's game against the Cubs, but that was the result of his 4 1/3 innings out of the 'pen on Friday.

Street rediscovering dominant form out of 'pen

CHC@SD: Street retires Murphy to tally his 25th save

SAN DIEGO -- Padres closer Huston Street is playing baseball's version of "chicken or the egg."

So which came first -- the confidence or the effectiveness? It doesn't matter much to San Diego manager Bud Black. He's just happy to see his closer finding the same groove he seemed to have throughout the 2012 season.

"I'm seeing better arm speed in all his pitches," Black said. "With that, I think you're seeing an uptick in velocity. The spin on the slider is much better.

"And because the results are better, his confidence is high. When any player is playing with confidence, that's a great mental edge."

Street is certainly pitching with an edge of late. After firing a scoreless inning on Sunday, he hasn't allowed a run in his last 17 1/3 frames, the longest streak by a Padres reliever this season. During that time, he has lowered his ERA from 4.78 to 2.89.

Street has been incredibly efficient, too -- an invaluable trait for any reliever. In his 16 consecutive scoreless outings, he has needed more than 15 pitches only three times.

"He's trusting his stuff," Black said. "That's what happens when things go your way."

Friar facts

• Outfielder Kyle Blanks was the designated hitter on Sunday for Tucson, where he played his first rehab game in his recovery from left Achilles tendinitis. He'll play the field on Monday.

Carlos Quentin will travel with the Padres to Arizona, and Black is hopeful his left fielder will be able to test his injured right knee by running sometime this week.

• When asked whether prospects Keyvius Sampson (RHP ranked No. 16) and Reymond Fuentes (OF ranked No. 17) might be called up when rosters expand, Black responded: "I don't know that you'll see both, but you'll see one of them, for sure."

• Left-hander Cory Luebke, who is recovering from Tommy John surgery in May 2012, will join the club on its road trip and throw two side sessions -- one Tuesday in Arizona and another over the weekend in Los Angeles.