The only possible explanation the Reds called up Alejo Lopez instead of Spencer Steer is this

The Cincinnati Reds placed infielder Mike Moustakas on the 10-IL on Tuesday with a calf strain and recalled Alejo Lopez. Many fans throughout Reds Country were hopeful to get their first look at Spencer Steer instead.

Steer was part of the trade that sent Tyler Mahle to the Minnesota Twins. Cincinnati also acquired power-hitting infielder Christian Encarnacion-Strand and pitcher Steve Hajjar.

Steer has spent his first week in the Reds organization at Triple-A Louisville and all he's done is rake. Steer is hitting .316 and had a wRC+ of 118 during his 48 games with the Twins' Triple-A affiliate earlier this season. So why did the Reds recall Lopez instead of selecting Steer's contract?

Why did the Reds recall Alejo Lopez and not promote Spencer Steer to the big leagues?

With the Cincinnati Reds now in midst of what we can officially call a rebuild, why in the world would they not give meaningful at-bats to a young player like Spencer Steer? Quite simply, this about the 40-man roster.

Steer will needed to be added to the 40-man roster this offseason in order to protect him from the Rule 5 Draft. But that's not necessary at this moment. The Reds are going to have a lot of crucial roster decisions in the coming months, and to make a transaction that would require a corresponding move at this time is not wise.

Adding Spencer Steer to the roster would've required the Reds to drop a player like Stuart Fairchild, Mark Kolozsvary, or even Alejo Lopez. The Reds seem unwilling to make that move at this point. It should also be assumed that Mike Moustakas' injury is minor, and he may very well return after the 10-day minimum. Had he hit the 60-day IL, fans may have seen Steer called up.

There's also not any room in the lineup for Steer to get consistent at-bats at the moment. The Reds had to move Kyle Farmer to third base in order to get Jose Barrero some reps in the big leagues. With Joey Votto and Jonathan India filling out the rest of the infield, at-bats would be at a premium for Steer. Donovan Solano is swinging a very hot bat as well

It wouldn't be surprising to see Spencer Steer added once the rosters expand in September. Reds fans might also get their first look at left-hander Brandon Williamson as well. However, both must be added to the 40-man roster in order to receive a September call-up, so that's still a concern.