KANSAS CITY -- The Royals made a series of roster moves ahead of Friday’s 5 p.m. CT deadline to add players to the 40-man roster, thus protecting prospects who were eligible for the Rule 5 Draft on Dec. 10. And some of the moves were at least mildly surprising.

To clear roster space, Kansas City designated right-hander Glenn Sparkman and left-hander Gabe Speier for assignment, and it also outrighted right-hander Chance Adams, who cleared waivers and was assigned to Triple-A Omaha.

Then, the Royals added four prospects to the 40-man roster: outfielder Khalil Lee, left-hander Daniel Tillo, catcher Sebastian Rivero and left-hander Angel Zerpa. Kansas City's 40-man roster is now at 40.

Lee, 22, was no surprise. He is the Royals’ No. 8 prospect per MLB Pipeline and was a cinch to be added. Kansas City believes Lee is on the cusp of cracking the Opening Day roster, as he has improving skills at the plate and in the field.

Lee was part of the Royals' 60-man player pool this past summer and flashed impressive skills during Summer Camp. He also impressed during the team's fall instructional league at Kauffman Stadium, according to club officials.

Lee has excelled at getting on base, posting a .382 on-base percentage in the Minors in 2018, and a .363 mark in '19. He's also shown natural power, hitting 17 homers for Class A Lexington in 2017. And although his power numbers dipped in 2019, when he hit eight home runs for Double-A Northwest Arkansas, the Royals believe Lee's power will continue to develop.

It also wasn't a surprise that Adams was outrighted. MLB.com learned that he underwent Tommy John surgery last month, essentially wiping out his 2021 season. The 26-year-old was once a top prospect in the Yankees' system, and he was acquired by the Royals in a trade last December. The righty appeared in six games for Kansas City in 2020, giving up nine runs on 15 hits in 8 2/3 innings.

Sparkman and Speier getting designated for assignment were mild surprises.

Sparkman, who was eligible for arbitration, attempted to convert to the bullpen in 2020, but he battled a right forearm strain and spent most of the season on the injured list. He had a 5.40 ERA in four games.

“It just didn’t work out,” Royals general manager Dayton Moore told MLB.com.

Speier, whom Kansas City acquired in a June 2018 trade with Arizona, appeared in eight games this past season and had a 7.94 ERA.

Another mild surprise was the addition of Tillo to the 40-man roster. The left-hander is the Royals’ No. 22 prospect and might have been considered a gamble to be taken in the Rule 5 Draft because he underwent Tommy John surgery this past summer and will likely miss much of 2021.

"It's easier for another team to hide those guys in his situation, now on the IL,” Moore said. “He's got electric stuff. He was ahead of [Tyler] Zuber for a bullpen role. He's got a chance to be really good, really special. We would have lost him [in the Rule 5 Draft]."

The Royals have been high on Rivero, 22, since signing him as an international free agent as a 17-year-old in 2015. He is a 6-foot-1, 200-pound defensive-minded catcher. But he hasn’t shown much power in the Minors, hitting .216 with a .553 OPS between Class A Advanced Wilmington and Triple-A Omaha in 2019.

Kansas City invited Rivero to Summer Camp, and he has been a non-roster invite to Spring Training the past two years.

Zerpa, 21, is likely the biggest mystery of the 40-man roster additions. He signed out of Venezuela in 2016, and has shown surprising command and advanced awareness on the mound for his age. He was 6-3 with a 3.40 ERA in 13 games (12 starts) in Rookie ball in 2019, striking out 55 and posting a 1.08 WHIP in 55 2/3 innings.

Moore said Zerpa will be known to fans very soon.

“He’s coming very quickly through the system,” Moore said. “He’s got great command, he competes. He’s right up there with [Daniel] Lynch and [Jackson] Kowar and [Jonathan] Bowlan and [Alec] Marsh, all of them. We would have lost him.”