With outfielders Dexter Fowler, Stephen Piscotty and Jose Martinez all out of commission, the Cardinals called up 21-year-old Magneuris Sierra to play center for the time being. Sierra was off to a fine start in High-A this year, hitting .272/.337/.407 through 20 games. But of course, all of that came against pitching that was not one, not two, but three levels below the big leagues.

Sierra’s hitting has never been his calling card, however, as his prosoectdom is centered around his speed and defense. Lead prospect analyst Eric Longenhagen described him as having “Gold Glove-caliber tools in center field” last month and gave both his speed and defense future grades of 70 over the winter. Those tools have translated to on-field performance in the lower levels, as he swiped 31 bags in Low-A last year and clocked in above average in center according to both Clay Davenport’s and Baseball Prospectus’ defensive numbers.

My KATOH system projects Sierra for 2.1 WAR over his first six seasons by the traditional method and 1.9 WAR by KATOH+, which integrates prospect rankings. Both are up slightly from the pre-season. KATOH recognizes Sierra’s speed and defensive prowess, but is underwhelmed by his offensive performance so far. He’s yet to hit for much power and doesn’t make up for that deficiency with good strikeout and walk numbers. Speedy, punchless outfielders who are just OK in A-Ball aren’t exactly rare commodities, so KATOH is not enamored with his future prospects. It essentially sees him as an underwhelming bench piece long-term.

To put some faces to Sierra’s statistical profile, let’s generate some statistical comps for the rookie center fielder. I calculated a weighted Mahalanobis distance between Sierra’s A-Ball performance and every A-Ball season since 1991. In the table below, you’ll find the 10 most similar seasons, ranked from most to least similar. The WAR totals refer to each player’s first six seasons in the major leagues. A lower “Mah Dist” reading indicates a closer comp.

Please note that the Mahalanobis analysis is separate from KATOH. KATOH relies on macro-level trends, rather than comps. The fates of a few statistically similar players shouldn’t be used to draw sweeping conclusions about a prospect’s future. For this reason, I recommend using a player’s KATOH forecast to assess his future potential. The comps give us some interesting names that sometimes feel spot-on, but they’re mostly just there for fun.

It appears as though Sierra’s ready to provide value on defense right now, though it’s far less clear what he’ll provide offensively. He’s yet to master A-Ball, which seemingly implies he’s nowhere near ready for the show. Longenhagen expressed tempered optimism about Sierra’s future offensive in the offseason.

Offensively, things are still evolving for Sierra, whose style of hitting was more slappy and opposite-field oriented early in the year and then more pull-oriented late in the summer. He has above-average bat speed and a little bit of bat control, but the quality of his at-bats is poor. Sierra regularly overswings, waves at early-count braking balls in the dirt, and just generally gives away at-bats. I think there’s a chance Sierra develops into some sort of offensive threat, either as a high-strikeout hitter who runs into a handful of homers every year or a squib-and-sprint type of bat.

However, he gave Sierra’s hit and power tools present grades of 20, which suggests even that modest level of production is a ways away. Sierra’s .247/.279/.331 rest-of-season Steamer projection tells a similar story. It’s conceivable that Sierra’s raw tools alone could result in an acceptable offensive performance. Stranger things have certainly happened. But the Cardinals will likely be content if he just provides them with good defense until their primary outfielders are ready to return.