"There's a ton of upside there," Baker said.
Cashner is 1-2 with a 4.50 ERA in his first three starts. He allowed four earned runs in four innings in his last start against the Cubs on May 1.
Cashner has displayed a live fastball in his first three starts and a good changeup at times, but for him to be successful moving forward, Baker said, he has to develop and trust another secondary pitch.
"It's finding a secondary pitch he can throw any time, especially when he's having trouble commanding his fastball," Baker said. "Once he does figure out what pitch that's going to be, it's developing the confidence to use it."
Two starts ago against the Giants, Cashner had a firm handle on his curveball, a pitch he used often in a victory when he allowed one run in six innings. But that curveball wasn't apparent in his last start against the Cubs when he struggled.
"In the bullpen, he can just throw his fastball by people," Baker said. "… But when you're throwing 100 pitches [as a starter], you can't do that."
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.