According to Greg Rajan of the Corpus Christi Caller-Times, Alberto Arias has a sore right knee, and so Wilton Lopez (from the Astros' AA team) will join the Astros in Phoenix for the D-Backs series, just in case Arias goes on the DL. 

Now, for scouting reports:

First, let's give credit to our resident prognosticator farm_stros, who predicted this callup nine days ago. In his previous post, farm_stros pointed out that

After four poor months, the Corpus Christi starter has the following line in four August starts: 29 2/3 IP, 14 hits, three runs, two earned, four walks, and 18 Ks.

and from BP's 2008 Prospect Guide

A former Yankee prospect who the Padres signed out of Nicaragua, righty Wilton Lopez is a sinker specialist who pounds the strike zone.

Luis Pujols, the manager of the CC Hooks says:

“Sometimes it’s not just the ERA – it’s what you see out there,” manager Luis Pujols said. “I believe he can do it. He’s throwing the ball well. I believe he can do it (in the majors).”

Lopez was acquired earlier this season when the Padres waived him after spring training.  A quick google search of Paul de Podesta's blog found a few brief comments that suggest Lopez throws pretty hard, topping out at around 94mph.

And one final tidbit:  An interview with Scout.com from 2007.

If Lopez works out, then kudos to the scouting staff who saw something they could work with and to Corpus Christi pitching coach Stan Boroski for polishing him up.