Marmol is being given a few days off to get back on track after a difficult week, including Thursday's game when he walked four and gave up a hit in a four-run ninth. He's now 19-for-26 in save situations.
"The only timetable I can say is he ain't pitching today," Cubs manager Mike Quade said.
Riggins said Marmol will throw on the side Sunday. The main mechanical tweak involves Marmol's grip on the ball. His hand has been more on the side lately than on top, and that needs to change.
"It's nothing major, just an adjustment," Riggins said.
Marmol has not struck out a batter since July 3, and that's unusual. Last season, he posted the highest single-season mark for a reliever, averaging 15.99 strikeouts per nine innings.
"His breaking ball is his strikeout pitch, and the breaking ball doesn't have the depth it had earlier in the year," Riggins said. "He's positive. He's going to be the same old Carlos here real soon."
Sean Marshall and Kerry Wood will take over the closer duties for now. Wood can relate to Marmol's struggles.
"He's an adrenaline guy who feeds off adrenaline when he comes in a game," Wood said. "It can be a good and a bad thing. A tendency for a guy with adrenaline when things speed up a little bit, it goes a little bit faster. Guys like Mariano [Rivera], when things speed up, he goes slower. But [Rivera] is not an adrenaline guy, he's a control pitcher. You know [Marmol] will bounce out of it and figure it out."
What's important is that Marmol has not lost confidence in his ability, Riggins said.
"He's very strong-minded," Riggins said. "If you're a closer, you're strong-minded. He wants to get back out there as soon as possible, and we want that, too."
Wood said it might help if Marmol returns and has a little more breathing room instead of one-run or tie ballgames.
"Those are tough for closers," Wood said. "Usually you get a handful of three-run opportunities a month, and not that it's easier, but you tend to work a little less. We've put him out there in tough spots.
"We're used to him getting out of anything. There's a little blip here and it's like, 'Oh, no, what has he done?' Everybody's allowed a rough stretch."
Does Wood want the closer's job back?
"No," he said quickly.