CLEVELAND -- The Royals' top pitching prospect, Kyle Zimmer, was placed on the disabled list on Sunday with right shoulder fatigue.

Zimmer, the club's No. 2 prospect overall and 60th-ranked prospect in all of Major League baseball according to MLBPipeline.com, has pitched 5 2/3 innings in the Minors this season between Class A Advanced Wilmington and Double-A Northwest Arkansas, allowing two runs (one earned) on four hits with 11 strikeouts in three starts.

The Royals' first-round Draft pick in 2012, Zimmer left his start for Northwest Arkansas on May 17 after only one inning due to shoulder fatigue. He also missed time during Spring Training with a similar shoulder issue.

Also on Sunday, the Royals signed infielder Irving Falu to a Minor League deal. Falu last appeared in the Majors in 2014, and previously played for the Royals in 2012 and 2013, hitting .337 (30-for-89) in 25 games.

Falu was signed because recently-singed infielder Steve Tolleson was placed on the DL.

Worth noting

• Royals shortsop Alcides Escobar is hitting just .189 in his last nine games after going 1-for-4 in Sunday's 7-0 loss to the Indians.

However, Royals manager Ned Yost didn't seem concerned, answering with a simple "no" when asked before the game if it was anything more than the normal ebb and flow of the season.

But Escobar isn't the only one slumping. Since his 14-game hitting streak ended, Paulo Orlando has one hit in his last 15 at-bats. Likewise, Lorenzo Cain -- who was given the day off on Sunday -- hasn't recorded a hit in his last nine at-bats. However, Yost has remained level, saying it was more of a factor of what the other team has been doing rather than anything else.

"I feel like we've faced two great pitchers the last two nights," Yost said. "We faced two pitchers [Danny Salazar and Josh Tomlin] on top of their game."

• After the passing of Muhammad Ali, Yost shared an experience of interacting with the boxer when Yost lived in Mississippi. He said he went to see Ali speak at Mississippi State, which made an impact on him.

"I can't remember the year ... right after he retired, he went on a speaking tour," Yost said. "I was dying to see him so I went."

Yost said Ali spent two hours sharing stories and answering questions. He said it was a "tremendous" and "phenomenal" experience.

The Royals also crossed paths with Ali before Yost became the manager. Ali visited with the team out in Arizona during Spring Training in 2009.

Scott Chasen is a reporter for MLB.com based in Kansas City.