CHICAGO -- It had become clear in recent weeks that Caleb Kilian's arrival to the Major Leagues was increasingly imminent. The only question was when and how Chicago would time the promotion of its top pitching prospect.

Cubs fans now have their answer.

"The Game 2 starter will be Kilian," manager David Ross announced after Friday's 14-5 loss to the Cardinals at Wrigley Field.

The Cubs will play host to the Cardinals in a doubleheader on Saturday at the Friendly Confines. Kilian will make his much-awaited Major League debut in the nightcap in front of a national audience, taking on a potent St. Louis lineup and pitching for a Cubs team mapping out its future blueprint.

As one of the prospects acquired from the Giants in the blockbuster Kris Bryant trade last summer, Kilian is an important piece to Chicago's long-term picture. There is a case to be made that his pending debut has been the most anticipated callup among Cubs pitching prospects in more than a decade.

"Caleb's got the full package, in my opinion," said Cubs catcher P.J. Higgins, who saw the pitcher first-hand with Triple-A Iowa and caught him some during Spring Training.

Kilian -- ranked No. 5 on MLB Pipeline's Top 30 Cubs prospects list -- came to Chicago as an arm capable of balancing power and precision. Across the High-A, Double-A and Triple-A levels in 2021 in the Giants' and Cubs' systems, he had 112 strikeouts against just 13 walks in 100 1/3 innings. Kilian spun a 2.42 ERA in the process.

The Cubs sent Kilian to the Arizona Fall League, where his development culminated with six perfect innings in the championship game for Mesa. He leans on a mix of sinkers, cutters and curves, and has been working on a changeup to add another layer to his repertoire.

“Once you get to Triple-A as a pitcher, so much of it is about refining your craft,” Cubs vice president of player development Jared Banner said last month. “He has the stuff, so it's about hitting your spots, executing game plans, things like that. And he's done a really good job."

Banner was asked what it would take for Kilian to finally get the call to Chicago.

"Keep dominating and make it obvious," Banner replied.

Through nine starts with Triple-A Iowa this season, Kilian logged a 2.06 ERA with 41 strikeouts and 15 walks in 39 1/3 innings. The Cubs controlled his workload early on, but built him up to the 75-80 pitch range in his last five turns. Kilian last started on May 25 and then had his next outing pushed back as the MLB team sorted through its options.

Lefties Wade Miley (left shoulder) and Drew Smyly (right oblique) are on the injured list, paving the way for righty Matt Swarmer to make his own MLB debut on Monday. Swarmer, who provided six effective innings against the Brewers, was looking forward to seeing his former rotation-mate in Iowa join him with the Cubs.

"It'll be a special moment for him, too," said Swarmer, who will start Game 1 on Saturday. "He's absolutely just dominating. Every time out, he was just competing his butt off and just throwing a lot of strikes, getting ahead in the count. He has a good mix of pitches."

Cubs righty Alec Mills is also on the IL and could be returning soon after his next Minor League rehab start on Tuesday with Iowa. In his time at Triple-A, Mills was also impressed with Kilian's pitch arsenal, adding that the young pitcher can be his hardest critic at times.

"I was telling someone the other day, he's better than he thinks he is, I think," Mills said. "I don't know if that's something he should probably know, but he's hard on himself. But he's always willing to learn. Super nice. Obviously, I'm super excited for him. It's a big moment. It'll be great for him."

Ross raved about Kilian's fastball, which can hit the upper 90's on the radar gun, and said the pitcher "has a pretty good energy about him." The Cubs have certainly experienced the latter from some of the other young players who have reached the big leagues this year.

To date, the Cubs have had seven players make their Major League debut this season. That has included the versatile Christopher Morel, whose single on Friday extended his on-base streak to 17 games to begin his career. Seiya Suzuki, Nelson Velázquez, Ethan Roberts, Brandon Hughes and Anderson Espinoza have also debuted this year.

"It's awesome having young guys that bring energy and go out there and perform," said veteran starter Marcus Stroman, who allowed nine runs in Friday's loss. "You feed off those guys as well and I think we have a great culture here. Any time we can get contributions from young guys, I think that's huge."

Now, it will be Kilian's turn.