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Callis examines Lopez, Houser and Weaver

Jim Callis breaks down the D-backs' Yoan Lopez, Brewers' Adrian Houser and Cards' Luke Weaver

SCOTTSDALE, Ariz. -- After Yoan Lopez's first season in pro ball, the Diamondbacks still aren't sure what they have.

They spent lavishly to sign the Cuban right-hander in January -- an $8.27 million bonus, plus a matching tax penalty for exceeding their international bonus pool -- then got only 54 innings out of him. He had blister issues early in the season and then got shut down in August with elbow soreness. In between, he left his Double-A Jackson team without permission the day before a start and then was found in Florida several days later. He made more headlines for hitting No. 1 overall Draft pick Dansby Swanson in the face with a pitch during a simulated game than he did in any contest that counted.

Arizona invested $16.54 million in Lopez believing that he could develop into a frontline starter, though some scouts with other clubs think he might not be more than a reliever. The reviews have been mixed in the Arizona Fall League as well.

During his first AFL start for the Salt River Rafters, Lopez dealt with a mid-90s fastball and a mid-80s slider for three innings before running out of gas in the fourth. In his second outing on Tuesday, a 3-1 loss to the Surprise Saguaros, his stuff wasn't nearly as impressive.

Lopez operated at 91-94 mph with his fastball, and while he threw 28 of 45 pitches for strikes, none of them elicited a swing-and-miss from the Saguaros. While he found the zone with his heater, it was fairly straight and he didn't use his 6-foot-3 frame to generate much downhill plane.

Lopez's slider looked like an average pitch at best, ranging from 79-83 mph with ordinary bite. He did catch Jose Trevino, the Rangers' No. 26 prospect, looking with a breaking ball for his lone strikeout, and his only two swings-and-misses in 66 pitches came from his slider. He threw a handful of changeups but they were too firm at 85-87 mph and he didn't seem to trust the pitch.

Surprise didn't exactly drive the ball against Lopez, but it did rough him up for three runs in 2 2/3 innings. Seven of the 15 batters he faced reached base (five singles, two walks), and the damage could have been worse if not for a baserunning mistake by Yadiel Rivera, the Brewers' No. 18 prospect. Lopez's performance certainly didn't make his uninspiring Double-A numbers (4.69 ERA, 32/24 K/BB ratio in 48 innings) seem like a fluke.

The Saguaros trotted out two starting pitching prospects who showed better than Lopez. Right-hander Adrian Houser, the Brewers' No. 27 prospect, earned the victory by opening with 3 1/3 scoreless innings.

Part of a bumper Oklahoma high school pitching crop in 2011 that also included Archie Bradley, Dylan Bundy and Tigers No. 1 prospect Michael Fulmer, Houser was a second-round pick of the Astros that June. He went to Milwaukee this July in the Carlos Gomez /Mike Fiers trade and made his big league debut in September.

Houser sat at 92-94 mph with life to his fastball, generating six of his 10 outs via groundballs, and he hit 95 on a swinging strikeout of Gavin Cecchini (Mets No. 4 prospect). His breaking stuff usually is more effective than his changeup, though on this day he showed better feel for the latter.

The day's best changeup belonged to right-hander Luke Weaver, the Cardinals' No. 7 prospect, who used it to record five of his nine outs. He allowed just a hit and a walk, though Salt River touched him for an unearned run thanks to a muffed grounder by third baseman Patrick Wisdom.

Weaver's fastball velocity was down in 2014, both at Florida State and in his pro debut after St. Louis drafted him 27th overall. He opened this season in extended spring training to build up his arm strength, then excelled in the high Class A Florida State League (1.62 ERA, 88/19 K/BB in 105 1/3 innings) once he got there in mid-May.

Against the Rafters, Weaver pitched at 93-95 mph in his first two frames and at 91-92 in his third. Even in the low 90s, his fastball maintained life and was effective setting up his changeup. He'll need to develop a better slider, which has been the knock on him for a while.

It's foolish to read too much into a single look at any prospect. But on Tuesday, Lopez didn't do anything to answer the questions that surround him. While Weaver showed the potential to become a No. 3 starter and Houser displayed possibilities as a No. 4, Lopez appeared destined for the bullpen.

Jim Callis is a reporter for Follow @jimcallisMLB on Twitter.

Read More: St. Louis Cardinals, Luke Weaver