SAN DIEGO -- The Padres have done a fair share of experiments in their rotation as of late, and they'll need to get even craftier as one of their rookie lefties prepares to come off the disabled list.
Eric Lauer will begin his rehab assignment in Lake Elsinore on Saturday, where he'll throw at least one start. He's expected to join the team before September, but because of the many off-days the team has that month, space in the trial-filled rotation is limited.
"We'll be monitoring performances and seeing how well guys pitch through the stretch of August," manager Andy Green said. "There's certain guys that are going to get opportunity no matter how they perform because we're committed to those guys. There's other guys where that opportunity depends on performance and how well they throw the baseball."
Lauer will join a rotation surrounded by question marks for the 2019 season, as all five spots are up for the taking. Clayton Richard -- the lone veteran in the current rotation -- is signed through 2019. He leads the team in innings pitched (150) and offers both experience and insight as a longtime Major Leaguer, but that might not make up for his 7-10 record and 4.98 ERA. Joey Lucchesi (6-6, 3.45 ERA) has put in a solid campaign in his rookie season despite missing nearly two months with a hip strain, but other rookies Brett Kennedy and Jacob Nix have made their Major League debuts this month and the team plans to continue taking looks at them as well.
Robbie Erlin has notched three consecutive solid starts, after being used for much of the season in long relief, and Green noted after his last start that he likes what he sees.
"He's doing what he needs to put himself in a rotation going forward," Green said.
The team also has Bryan Mitchell and Luis Perdomo on the disabled list. Although there is no exact timetable for either's return, Green indicated last month that Mitchell could get a chance to start again. He said Friday that for space reasons, Perdomo could be in the bullpen when activated.
"Where he is right now, I wouldn't see him back until Sept. 1," Green said. "We're going to be getting a lot of guys around that time that we're looking at to be starters for us, so it's definitely possible."

Lauer, who landed on the disabled list last month with forearm tightness, isn't worried about the logjam in the rotation. He's just excited to be able to compete again, saying he didn't want to go on the DL -- although the Padres stressed they were going to rest the young southpaw at some point in the second half.
"Nobody wants to go on the DL," Lauer said. "I thought I could've kept pitching through it, but they said, 'We're going to be a little more cautious.' I think the rest has helped me, and I think it'll help me finish strong.
"I'm just excited to get back into competition. I'm really just going to use it as a jumping-off point to get back in the rotation. I'm not looking for anything specific or setting any goals. I'm just looking to get through with no pain, no nothing, which, I'm not expecting any pain. I haven't had pain for a week and a half."
Makita optioned, Diaz recalled
The Padres optioned reliever Kazuhisa Makita to Triple-A El Paso before Friday's game and recalled right-hander Miguel Diaz. Makita threw 3 1/3 innings of scoreless relief in Thursday's 5-1 loss to the Diamondbacks.
"Tough to lose Maki after he threw the ball really well for us yesterday," Green said. "It's just what happens sometimes, you need to refresh your bullpen."

Diaz has appeared in just one game for the Padres this season, but left a memorable impression, striking out five batters in two scoreless innings.
Trey OK, cleared to pitch
Trey Wingenter had to be removed from Thursday's game after being struck by a comebacker on his pitching arm, but has been cleared to pitch and will be available for Friday's game.
"In an ideal world we don't have to use him, but I'll check in with him before the game and see where his head's at," Green said.