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5/30/2014 11:00 P.M. ET

Duffy set to face Cardinals; Chen progressing

TORONTO -- "Dead arm" or not, left-hander Danny Duffy plans to be full of life on Monday night at St. Louis when he faces the Cardinals.

After Duffy lasted just four innings and gave up six runs in Wednesday's 9-3 loss to the Astros, manager Ned Yost called Duffy's problem a "dead arm."

"Nothing was coming out. He didn't call it dead arm, it's just that he was throwing it as hard as he could and it was coming out 90, 91 [mph]," Yost said. "It was the best way that I could describe it."

Duffy was sort of baffled by the whole thing.

"My velocity dipped pretty drastically compared to the prior start, but I think it's just something that all pitchers go through every now and then," he said. "The good ones pitch through it and get outs anyway, and I didn't. So depending on what I've got in the tank on Monday, I'm going to make better pitches. I can get outs no matter what and there are no excuses for giving it up like I did."

So puzzled was Duffy that he found himself looking at the radar gun readings from the mound.

"It's weird," he said. "I don't normally peek at the velocity on the scoreboard. But I knew it wasn't coming out good and I was trying to get behind it as much I could. And I was looking and I'm like, man, 88, 87, 90 and I didn't know what was going on. I've never had that before. So, I was done and I tried to put more behind it as opposed to just working with what I had that day."

Duffy has made five starts since taking over for sore-backed Bruce Chen. Finally, Chen is making solid strides toward returning to the Royals.

"Bruce threw a simulated game today and looked very good," manager Ned Yost said on Friday. "He's probably going to go out on rehab. He'll throw another side session here on Sunday and then if he passes that test, he might be ready to go out."

When Chen does report to the Minors, he'll probably need at least three starts to build up his arm strength and pitch count so he can return as either a starter or reliever, depending on the club's needs at that time.

"I don't anticipate him having any setbacks. He looked good today, felt good today," Yost said.

Chen threw two 15-pitch innings at Rogers Centre, facing hitters Jimmy Paredes, Brett Hayes, James Shields and Duffy.

"He humbled Duffy real quickly," Yost said. "Duffy thought he was a good hitter until he faced Bruce. He walked out a little defeated."

Duffy will get another test on Monday night when he gets in the batter's box against the Cardinals' Shelby Miller.

Royals tab Brooks for Saturday start vs. Toronto

TORONTO -- Saturday's starting pitcher for the Royals is no longer a mystery. It'll be right-hander Aaron Brooks, who will be called up prior to the game from Triple-A Omaha.

This won't be Brooks' first rodeo. He got a rough initiation on May 3, courtesy of the Detroit Tigers. That's the night he made his Major League debut at Kauffman Stadium.

With the Royals trailing, 3-0, Brooks became the Royals' fifth pitcher of the game. He got through the eighth inning without a problem. He retired the first two hitters, Victor Martinez and Torii Hunter, before Austin Jackson doubled. Then, Brooks made Nick Castellanos his first strikeout victim.

However, the ninth inning proved to be a six-hit, six-run pounding. It culminated with Hunter belting a three-run homer in what became a 9-2 Tigers victory.

Brooks had better success with Omaha, going 4-1 with a 3.12 ERA in eight games. In 40 1/3 innings, he has 24 strikeouts and eight walks.

"He's been throwing good. He's a kid that's not afraid. Throws strikes, commands the ball. A simple decision," Royals manager Ned Yost said. "That's who they recommended; we had a lot of people in there watching."

Brooks takes the spot left open when rookie Yordano Ventura experienced elbow problems in his last start and left a 9-2 loss to the Astros in the third inning. Yost decided to skip Ventura's scheduled Saturday start as a precaution.

Valencia back in lineup after five-game break

TORONTO -- After missing five straight games with a left hand sprain, third baseman Danny Valencia was back in the Royals' lineup on Friday night against the Blue Jays.

"I'm just going to play and play through it," Valencia said. "Obviously, it's not going to be pain-free, but this is the time of year where everybody's playing with something. And you want to be out with the guys so I'm just going to go and do it."

Valencia played the entire game and went 0-for-4 in the Royals' 6-1 win.

Valencia wants to make the most of his playing time while Mike Moustakas is away with Triple-A Omaha, trying to solve his hitting woes. Moustakas, through Thursday, was batting .296 in seven games.

Moustakas went 3-for-4 in Thursday night's 5-3 win at Oklahoma City with two doubles -- one that cleared the bases. One of the doubles was a line drive to left field, good news for the Royals who want the left-handed batter to hit the ball to the opposite field on occasion.

There's no set timetable for Moustakas' return to the Royals.

"He comes back when he comes back," Yost said. "[Royals senior advisor] Donnie Williams went and watched him play last night, and said he was all over the field and looked great."

Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.