HOUSTON -- While the Mariners are going with a four-man rotation for the moment after trading Mike Leake and having some extra off-days in the schedule, manager Scott Servais said Sunday that the club eventually could shift to a six-man group in September when rosters expand.

With top prospects Justus Sheffield and Justin Dunn both expected to be added by late August or the start of September, the Mariners will be able to alleviate the workload on Yusei Kikuchi as they look to keep his innings limit in check this first year in the Majors.

There’s also a chance that Félix Hernández will return at some point in the final month as he ramps up his rehab from a shoulder issue that has sidelined him since mid-May.

Kikuchi has currently thrown 118 innings and is on pace for 169, which is about where the club wanted him to be after coming over from Japan. No. 1 starter Marco Gonzales has thrown 139 2/3 innings and is on pace for 200 for the season, well above last year’s 166 2/3 innings, so he could also benefit from an expanded rotation in the final weeks.

The two other Mariners starters -- veteran lefties Wade LeBlanc and Tommy Milone -- will continue being used behind openers.

Servais isn’t worried about Gonzales, who has been throwing very well. But there is concern with Kikuchi, who has gone 1-7 with a 7.65 ERA over his past 12 starts. The Mariners initially planned to have Kikuchi go just one inning or skip a start about once a month this initial season in the Majors, but he’s done that just twice so far.

“We could still do that or just give him more of a break by going to six at some point, once we get to September,” Servais said. “We’ll talk about it when we get back home. He has to continue to grind through it and learn from it and make adjustments. We could give him a spot or short start, but right now we’ll keep him where he’s at and there’s a chance we go to six in September.”

Kikuchi threw a career-high 187 2/3 innings in 26 starts in 2017 and 163 2/3 last year in Japan, but the Mariners want to get him in the 160-170 range this year and then build him to 200 next season.

“It’s just a different schedule here than Japan, having to pitch more frequently and maybe a little more stressful innings,” Servais said. “We have to be patient with this. We said from Day 1 it’s a developmental year for him. There have been some good signs and some outings that haven’t been as good. He will learn from it.”

Worth noting

• Second baseman Dee Gordon did some pregame running on Sunday and again had no issues, as he works back from a strained left quad muscle that has sidelined him since July 22. Though Servais previously had indicated Gordon likely would need a Minor League rehab game or two, he said Sunday that it’s possible Gordon could just be activated on Tuesday when the club opens its next homestand against the Padres.

• Brandon Brennan, the Mariners’ rookie reliever who they selected in the Rule 5 Draft, threw another scoreless inning for Triple-A Tacoma on Saturday as he also appears ready to return from a right shoulder issue that has sidelined him since June 14. In eight appearances with Tacoma, Brennan has allowed one earned run and four hits with nine strikeouts and four walks over 7 2/3 innings.