The Cubs called up left-hander Brian Matusz from Class AAA Iowa to start Sunday night against the Mariners and give the Cubs’ starters an extra day of rest.

“As we’ve talked about, [we’re] attempting to give our regular five a rest at a particular moment,” manager Joe Maddon said. “It’s possible. It’s not impossible.”

To make room for Matusz, the Cubs optioned reliever Justin Grimm, who has struggled for most of the season. He has a 4.72 ERA in 34⅓ innings, but in his last seven outings (5⅓ innings), he has allowed no runs and two hits with seven strikeouts.

The Cubs have used a spot starter once this season, when Adam Warren took the loss against the Reds on July 6. Warren, who was acquired from the Yankees, was traded back to the Yankees as part of the deal for closer Aroldis Chapman last week.

The Cubs’ rotation leads the majors in ERA at 3.01. Still, Maddon believes the additional rest won’t hurt. Some of the Cubs’ veteran pitchers, including ace Jake Arrieta, bristled at the idea in early June but since have eased up.

“We use that [extra] day however we need to,” said Arrieta, who allowed two runs and two hits in seven-plus innings and took the loss Saturday against the Mariners. “At this time of year, every one of us might need to refine something, so an extra day might not be a bad idea.”

The Cubs signed Matusz on June 14. The Orioles traded him June 1 to the Braves, who released him. In two starts at Iowa, he gave up two earned runs in 9⅓ innings (1.93 ERA) with 11 strikeouts and three walks.

Matusz, 29, was drafted fourth overall by the Orioles in 2008. In 2010, he went 10-12 with a 4.30 ERA in 32 starts. He was moved to the bullpen in 2012.

Arrieta, a former Oriole, is familiar with Matusz’s game.

“I’ve seen him pitch extremely well,” Arrieta said. “He’s a smart guy who has got some really good pitches that he knows how to use effectively. Hopefully he can come here ready, and we can move forward.”

Maddon has addressed the idea of a six-man rotation before and said he can see it happening more down the stretch.

“This is also about the schedule,” Maddon said. “Built-in off days are coming up. We still want to take advantage of this, knowing it is going to get really hectic, the later part of August and early September. If the opportunity is there, take advantage of it.”

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Email: jtolentino@suntimes.com