VERO BEACH, Fla. -- While Brad Penny inches closer to game action, Dodgers management is scrambling to find someone to pitch in his place.

Initially, that would be the fourth game of the regular season in Arizona, and the Dodgers might not know who will take the ball until it happens.

Penny will start the season on the disabled list, pitching in the minor leagues, and an unofficial target date for his return might be April 20, the second time a fifth starter will be needed. The trade of Kazuhisa Ishii made Wilson Alvarez the preferred option to fill in for Penny, but a stiff shoulder has Alvarez doubting whether he will be ready.

"It will be tough," said Alvarez, who might join Penny on the disabled list to start the season. "I played catch today, but had nothing behind it."

If Alvarez is disabled, unlikely names would start the season on the active roster. Rule 5 draft pick D.J. Houlton is a strong possibility, despite his appearance Friday in which he allowed two runs on six hits in 1 2/3 innings.

"I'm not disappointed at all," Tracy said of Houlton's outing.

There should be room on the roster for at least one of two non-roster situational left-handed relievers, Kelly Wunsch or Mike Venafro, maybe both. Non-roster starters Ryan Rupe and Buddy Carlyle haven't been eliminated yet, either, as the club is almost certain to carry 12 pitchers.

The rotation for the three-game San Francisco series shapes up as Derek Lowe, Odalis Perez and Jeff Weaver, assuming Perez's shoulder is fit, which he says it will be.

"I know I'll be fine. Everything will be good," said Perez, whose second game appearance will be Sunday. "I will be ready."

Scott Erickson will probably start the fifth game of the year in Arizona, but the fourth game has plenty of candidates.

Elmer Dessens will pitch in a minor league game Saturday to build up his pitch count in case he gets the call in Penny's slot. Dessens was the surprise starter of last year's division title-clinching game, but was long gone by the time Steve Finley beat the Giants with his grand slam. Giovanni Carrara already has an outing of 2 1/3 innings.

All of the maneuvering, of course, is to bide time for Penny, who is returning from the arm nerve injury that wiped out most of the last two months of the season. Physically and mentally, he's getting closer.

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The original plan for Penny on Friday was one inning in a minor league game, but an audible was called and he instead threw batting practice with the intent of re-creating the ups and downs of multiple innings.

After 36 warmup pitches in the bullpen, Penny made 15 pitches to Cody Ross and pitchers Jeff Weaver, Alvarez and Perez. Then he sat down for eight minutes, warmed up again and made 15 more pitches to Ross, Perez and Alvarez.

After another eight-minute break, he warmed up again.

"Today they wanted me to throw in a game, but they left it up to me," said Penny. "That right there felt good. I just wanted to make sure, I wanted to go out and sit down and get back up. Today was the biggest day for me, to be able to get loose and not tighten up."

Although the club is eager to get Penny in a game, it was not clear whether that would be the next step or another batting practice session.

The difference?

"Adrenaline, mostly," said Penny.

He said he is using his changeup more and is hopeful that will save some stress on his arm.

"I don't know how hard I'm throwing, but it feels good coming out of my hand," Penny said. "They're saying I'm throwing pretty hard."

They being the pitchers he faced, and yes, he is.

"His fastball has a lot of life," said Perez. "I believe he's almost ready for a game."

Dioner Navarro, who caught Penny, estimated his fastball range from 90-95 mph.

"I was telling the pitchers what was coming and they still weren't catching up to it," Navarro said.