CLEVELAND -- The Guardians' starting rotation remains under construction.

Cleveland optioned left-hander Logan Allen to Triple-A Columbus on Sunday, one day after he struck out a season-high nine in 4 innings against the San Francisco Giants.

The somewhat surprising move comes a week after the American League Central leaders sent Triston McKenzie down to the Clippers following struggles in recent starts.

Allen is 8-4, but he has a 5.67 ERA in 18 starts. On Saturday, he allowed just two runs but walked four.

Manager Stephen Vogt said the club needs more consistency from Allen.

"We've seen it where he'll have one outing where he's efficient, he's filling up the strike zone," Vogt said. "He goes six innings, and then he'll have one where it kind of struggles, a lot of pitches, struggles to find the strike zone and doesn't quite make it that far.

"We just felt like this is a time for you to go down, take a deep breath, continue to work on those things, get back to being the best version of you."

Allen's demotion clears a roster spot for Spencer Howard, who was acquired in a trade from San Francisco on Friday. Vogt said the club has yet to determine when Howard will make his debut.

Howard went 1-1 with a 5.63 ERA in seven appearances (two starts) for the Giants.

Allen's turn would be Thursday, when the Guardians are in Detroit.

The Guardians have been juggling their rotation since the start of the season. Ace Shane Bieber made two starts before he was shut down to have Tommy John surgery. Gavin Williams made his debut last week after an elbow injury in spring training.

Cleveland recently signed free agent left-hander Matthew Boyd for the remainder of the season, but he won't be ready until August after undergoing elbow reconstruction last year with Detroit.