SAN DIEGO -- Very little is certain in the Padres' rotation entering the 2018 season.
Clayton Richard is back, having inked a two-year, $6 million extension. Luis Perdomo and Dinelson Lamet will get an opportunity to win their places. But the lack of depth is glaring, and general manager A.J. Preller has plenty of work to do.
"Clayton coming back gives us some depth, but when you're really successful, you get to a situation where you have starting pitching depth at the big league level and at Double- and Triple-A," Preller said. "We're getting closer to that point. That Double-A rotation was six deep in prospects. Those guys need to take another step. ... But you can never have enough starting pitching. I know it's a cliche, but it's definitely true for us."
The Padres will pursue at least two Major League-caliber starters in free agency. Here's a look at the current state of the 2018 San Diego rotation.
Locks (1): Richard
Richard posted a 4.79 ERA in 197 1/3 innings last season. He was on the wrong side of some tough luck, as the Padres' beleaguered infield defense did little to help Richard, a ground-ball machine.
It's conceivable that Richard finds himself in the bullpen by the end of his deal. But the Padres value his presence as a leader in the rotation, and they could use similar durability in 2018.
Probably in (2): Lamet, Perdomo
It's hard to envision a rotation without Lamet and Perdomo come April. The Padres are constructing their roster with one eye on the future, and Lamet and Perdomo could be integral in that regard.

Based on performance, Lamet's spot is probably safer. He posted a 4.57 ERA, only 10 points better than Perdomo. But that mark dipped to 3.80 during the second half. Lamet's 10.9 K's per nine innings were the most in Padres history for a rookie with at least 100 innings.
Perdomo, meanwhile, is set to embark on a crucial season in his trajectory. He cracked the big leagues earlier than anticipated, in 2016, because of his Rule 5 status. Some of his struggles can be attributed to that. But entering his age-25 season, Perdomo's early arrival is no longer an excuse.

Back from injury (3):Matt Strahm, Robbie Erlin, Colin Rea
The biggest question marks come in the form of Strahm, Erlin and Rea, none of whom pitched for San Diego last season. Rea and Erlin are coming off 2016 Tommy John surgery and Strahm, a non-waiver trade Deadline acquisition, is coming off July surgery on his left knee.
The three should be healthy come March, and will compete for roster spots. Rea and Erlin are viewed exclusively as starters, but the Padres have yet to determine a role for Strahm.

"He gives us versatility," Preller said. "We've talked about his role, but the biggest thing right now is to make sure that he's healthy. Then we'll figure out the exact role."
Bullpen-bound? (1):Travis Wood
If Wood wants a place in the rotation, he's got an uphill climb. In '15 and '16, he pitched out of the Cubs' bullpen to a 3.50 ERA and more than a strikeout per inning.

A lefty who can pitch multiple innings and serve as a spot starter, Wood could be a useful addition to the relief corps. But coming off his 6.80 ERA in 2017, it's unlikely he's back in the rotation.
Free agents
The Padres have indicated they'd like to bring back Jhoulys Chacin. But even if he returns, they're probably looking for one or two more big league-caliber starters.

A year ago, Preller signed four free agents to affordable one-year deals. Chacin and Richard were effective, while Trevor Cahill was dealt to the Royals in the deal that netted Strahm. Only Jered Weaver flopped.
With an impressive Double-A rotation waiting in the wings, Preller appears ready to approach this free-agent class the same way. He'll be looking for affordable short-term options -- likely pitchers with upside who can prove their worth in San Diego on one-year deals.