SAN DIEGO — The A’s are playing an interleague series in a National League ballpark, meaning they’re without the use of a designated hitter.

Commissioner Rob Manfred hinted last week that there’s momentum toward making the DH rule universal, but A’s manager Bob Melvin, a former catcher who played and managed in both leagues, still prefers the status quo.

“I like the differences in the leagues,” Melvin said. “I think that’s what makes each league unique. I’d be for keeping it the same.”

Melvin realizes the injury risk when his pitchers pick up a bat, including Paul Blackburn on Tuesday and Frankie Montas on Wednesday. Yankees pitcher Masahiro Tanaka recently went on the disabled list after injuring his hamstrings running the bases.

“There is definitely a disadvantage for American League teams going into a National League park,” Melvin said. “You don’t want to overdo it with these guys. … We’re always kind of holding our breath when our pitchers are at the plate and, hopefully, on the bases as well.”

Melvin said he’d like one change with the DH in interleague play, using NL rules in AL parks and vice versa “to get the fans a little different look.”

Chapman’s hand: Matt Chapman, who’s on the disabled list with what the team is calling a right thumb contusion, had a cortisone shot, and the A’s hope he’ll respond favorably and swing a bat Thursday.

Photo: Scott Strazzante, The Chronicle

“We’re waiting to see if that takes care of it over the next couple of days,” Melvin said.

Chapman dealt with a hand ailment late last season and in spring training, and the A’s are looking for clarity and a resolution so it doesn’t continue bothering him into the summer.

The A’s didn’t want Chapman to swing a bat again until he saw Dr. Steven Shin (of the Kerlan-Jobe clinic in Los Angeles), who detected issues similar to what bothered Chapman in spring training. He also saw Dr. Vernon Williams, a neurologist, at the same clinic.

Briefly: Matt Joyce (strained back) had three hits for Triple-A Nashville on Tuesday and is expected to rejoin the A’s this weekend in Chicago. ... The Padres bumped former A’s pitcher Tyson Ross back a day so he won’t face his old team Wednesday. Instead, rookie Joey Lucchesi, who played at Newark Memorial High and Chabot College and grew up an A’s fan, will come off the DL to make the start.

John Shea is The San Francisco Chronicle’s national baseball writer.