Jackson said after Sunday's start that he didn't expect the cramp to affect his next start. Manager Tony La Russa echoed that feeling Monday.
"Physically, sometimes that cramp is really deeper in there or it's a strain, but it doesn't appear to be," La Russa said. "They put pressure on it after the game, and it responded well."
In other injury news, infielder Nick Punto began taking ground balls on Sunday, but he did not travel with the team to Pittsburgh and is not yet able to take batting practice.
"He's improving, he's doing different kinds of drills, but he's still not 100 percent clear to take BP or even throw," La Russa said.
Punto has been on the disabled list since July 29 with a strained left oblique. He said Thursday he hopes to be back with the team within the next three weeks.