• Cardinals' Top 30 prospects
"He saw him go get a couple balls and said, 'This kid can flat play,'" Matheny explained. "[I told him] the only problem is [Sierra] has only played in low-A ball, which kind of blew him away."
Matheny, too, has singled out Sierra as among the most impressive young players in camp. Sierra has not only opened his first stint in Major League camp with six hits in 15 Grapefruit League at-bats, but he has showcased his speed on the bases and in the outfield.
He had a web gem in center field against the Braves on Tuesday and made an over-the-head basket catch look routine against Washington on Saturday. Over the past few days, Matheny has used the words "electric" and "exciting" to describe the outfielder.
Sierra spent 2016 with low-A Peoria, where he hit .377/.335/.395 with 31 stolen bases in 122 games. The Cardinals added him to the 40-man roster in November to protect him in the Rule 5 Draft.
Catcher Yadier Molina will play in his seventh Grapefruit League game on Sunday and then head west for the World Baseball Classic. Molina will report first to Arizona, where he'll participate in exhibition games with the Puerto Rican team, before traveling to Mexico for the first round of the tournament.
Molina is one of five players slated to depart Cardinals camp over the next two days because of World Baseball Classic commitments. Carlos Martinez (Dominican Republic), Alberto Rosario (Dominican Republic), Rowan Wick (Canada) and Trey Nielsen (Italy) are also headed out. Seung Hwan Oh (Korea) and Corey Baker (Israel) left last weekend.
Reliever Brett Cecil will remain in camp for now, but he could be summoned by Team USA, if it advances beyond the first round.
Odds and ends:
• Jedd Gyorko drew the start at first base on Saturday. He started eight games at first last season, but the Cardinals want to get Gyorko work across the infield this spring so he's ready to play anywhere. Gyorko exited the game after being hit by a pitch on his right arm, but the issue wasn't considered serious.
• Arturo Reyes notched his second scoreless appearance of spring and elicited some praise from his manager afterward.
"He's a guy who maybe is undervalued in this mix when you talk about all of our young arms," Matheny said. "He's got a real nice idea how to pitch."
Jenifer Langosch has covered the Cardinals for MLB.com since 2012, and previously covered the Pirates from 2007-11. Read her blog, follow her on Twitter, like her Facebook page and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.