Rookie center fielder Cedric Mullins would have been one of the most interesting Orioles storylines during Sunday night’s nationally televised game against the New York Yankees if he hadn’t woken up with a sore hip Sunday morning.

Mullins was not in the starting lineup and is day-to-day for the three-game series against the Toronto Blue Jays that starts tonight at Oriole Park.

He isn’t sure exactly what caused him to “tweak” his hip, but it was sore enough for him to call the Orioles’ training staff first thing Sunday morning.

“There’s a little fatigue involved,” he said. “Having to go through my second nine-inning doubleheader, it was just a long day. This will give me some time to recover. I’m kind of banged up from it.”

Mullins is off to a very good start at the major league level, hitting safely in 10 of his first 15 games (.309). He also has played strong defense and went well above the fence in Saturday’s first game to rob slugger Giancarlo Stanton of a home run.

Whether it was that play or some other that caused the hip strain is unclear.

“He’s not sure exactly which play, thought it was probably on a throw he made, kind of an off-balance, awkward throw,” manager Buck Showalter said. “It improved as the day went on — call it a hip flexor. I just didn’t want to linger on.”

Showalter on O’s rebuild: Showalter on Sunday reflected on the year that took the Orioles from wild-card contenders to one of the worst seasons in baseball history, and as the team’s rebuild is pitched to a national primetime audience on ESPN’s “Sunday Night Baseball,” there was one word he kept coming back to: hope.

“I think hope is a great thing,” Showalter said. “Hope. It’s kind of similar to when I first came here. You’ve got to know who you are and how you’re going to do it and stay true to it and be honest with the fans, [saying] ‘Here’s what we’re going to do, here’s how we’re going to do it and stay with it,’ and you’ll get a return for it. And when? If you think that I wouldn’t go into next year trying to win as many games as possible and see what could be…”

The Orioles have been publicly leaning into their status as a rebuilding club since last month’s trade of All-Star Manny Machado, who was quickly followed out the door by Zach Britton, Brad Brach, Darren O’Day, Kevin Gausman and Jonathan Schoop.

“It’s funny, we have more analytical ways to evaluate players than ever before, but it seems like there’s more mistakes being made on players than ever before,” he said. “Sometimes, I think that we have all this stuff that analytically, physically, you can put your hands on, what a guy can do down a line or his range or whatever. But it seems to be still a challenge to identify the human element.”

Gentry, not Jones, in CF:Craig Gentry started in center field in place of Mullins and Adam Jones remained the starting right fielder. Showalter explained that he and Jones agreed that the move to right field would be permanent.

History class: When the Orioles get to Kansas City next weekend, Showalter said that he’ll take the team to the Negro Leagues Baseball Museum. “They need to see that,” he said. “It’s very moving.”

peter.schmuck@baltsun.com

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Baltimore Sun reporter Jon Meoli contributed to this article.