There has been no question about the impact Magnerius Sierra has made since making his debut with the St. Louis Cardinals. The rookie has batted .353 (6-17) and scored 7 runs in the four games he’s played. And even though he has yet to steal a base, his speed has forced opposing defenses into rushing plays and making mistakes.

So with all of that taken into consideration, Mike Matheny had to decide which of his four available outfielders would start tonight against Chicago. He chose Tommy Pham in left, Dexter Fowler in center, and Randal Grichuk in right.

“Never easy,” said Matheny. “I put a lot of thought into it every day. Today was no different.”

So for tonight, Sierra will watch his first game in the big leagues from the bench.

“Be ready to come in in whatever situation,” said Matheny. “Obviously, he brings a speed component like we don’t have on this team. You don’t see much of a defensive replacement when you have a Grichuk and a Pham and a Fowler in the outfield. But there’s a double-switch possibility. There’s coming in and taking a quality at-bat or going in and running the bases. He’s just going to need to stay on point all game long.”

But while he’s on the bench tonight, Matheny also wasn’t ready to assign Sierra that role moving forward.

“He’s not a bench player right now,” stated Matheny. “He’s played every day, up till today, since he’s been here. He just needs to keep learning, keep watching, keep getting better and take advantage of the opportunities when he gets them.”

The issue is actually part of a bigger question the St. Louis Cardinals will soon need to answer–where does Sierra play moving forward? Fowler is back in the lineup tonight. Stephen Piscotty is likely to begin a rehab assignment next week and Jhonny Peralta will be finishing his soon. Those are two roster spots that will have to be accounted for.

At only 21 years old, there is an argument Sierra needs to still play as much as possible and that opportunity may only come by returning to the minor leagues.

“As all of you historically know, my opinion on young players sitting on the bench up here is not something I’m a big fan of,” said John Mozeliak. “But I would say that given the impact he had over the past week and the experience and some of the nuances that he’s getting to learn, I think it’s valuable.

“But at some point we’re going to have to make roster decisions, right? We just talked about two position players who are going to begin rehabs in the next couple days. At some point, they’re going to be ready to come back. For him to get a taste of what this is all about, I’m ok with that.”

Watching how veterans train and prepare at the big league level is part of the education Mozeliak is looking for Sierra to benefit from even if not in the starting lineup.

“Obviously, you wouldn’t want to say that over the course of a month,” pointed out Mozeliak. “But for a week to 10 days, I think that’s perfectly acceptable.”