KANSAS CITY, Mo. -- Yordano Ventura will be back Tuesday for the Kansas City Royals and Brayan Pena figures to be added to the St. Louis Cardinals' active roster.

The Cardinals, however, might be without shortstop Aledmys Diaz, who fouled off a pitch near his right eye in the ninth inning.

Ventura will have 10 days between starts. He has not pitched since June 17, working 6 1/3 scoreless innings without a walk to beat Detroit. The next day, however, Ventura dropped his appeal of a nine-game suspension after it was reduced to eight games.

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Major League Baseball suspended Ventura from a June 7 incident when he hit Manny Machado with a pitch at Baltimore. Machado charged the mound, threw a punch and the dugouts and bullpen emptied.

How rusty will Ventura be after the layoff?

"Eight games are not that huge of a layoff," Royals manager Ned Yost said. "We're going to face that when we come back from the All-Star game. Guys are going to be six, seven, eight days in between (starts)."

Ventura did have a two-inning simulated game during his time off.

"We tried to provide him an opportunity, where he could face hitters," Yost said. "He threw 30 pitches. He threw all of his pitches. Ventura will be ready to pitch tomorrow."

Ventura lost to the Cardinals twice last season, 6-2 on May 24 at Kansas City and 5-0 on June 12 at St. Louis. He is 1-2 in three career starts against the Cardinals, but the Royals have supported him with a total of four runs in those starts.

The Cardinals signed Pena to a two-year contract to be a veteran reliable backup to All-Star catcher Yadier Molina. But Pena, who played with the Royals from 2009 to 2012, suffered a knee injury and had surgery in April. He has missed the first 75 games.

Pena had 10 hits, all singles, in 52 at-bats in 14 rehab games with Triple-A Memphis and Double-A Springfield (Mo.). He drove from Springfield to Kansas City to join the club Monday but was not reinstated.

After catching complete games three straight days, the Cardinals opted to give Pena another day before reinstating him.

"I think we're close," Cardinals manager Mike Matheny said of activating Pena. "Obviously, he's here. Yesterday, he had four at-bats, take a little more rest today and have him looked over and see what we do from there."

Pena said the knee is fine.

"My personal goal was every time I left the baseball field, I wanted to feel pain-free," Pena said. "I accomplished that. I really feel excited about. I was really pushing myself very hard to see where I was at, and my knee really responded well."

The Cardinals are uncertain how Diaz's eye will respond or how soon. He was taken to the hospital to check his vision after the 6-2 loss to the Royals.

"I hope it's just a scare," Diaz said through an interpreter in the clubhouse before going to a hospital. "Obviously, when the inflammation goes down, I hope to be able to keep helping the team. Right now, it just hurts where I was hit.

"We are going to the hospital to do some more routine exams just to make sure everything is OK."

He said he was not dizzy nor were there were any concussion symptoms.

"Thanks God, no," Diaz said. "Just simply the inflammation and discomfort."

Diaz is hitting .316 with 21 doubles after getting two more Monday.

"It didn't look there was anything to worry about as far as a fracture," Matheny said.

Cardinals right-hander Michael Wacha, who is 1-1 with a 1.80 ERA in three career starts against the Royals, will start Tuesday.