Wojciechowski, 26, is rated by MLB.com as the Astros' No. 22 prospect. He was 6-2 with a 5.42 ERA in 15 starts for the Grizzlies this year.
"I thought I was competing well," he said. "I was coming off a couple of rough outings where things didn't really go my way, but stuff-wise I felt good. I felt like I was really working on my pitches and getting better. I felt like just these last couple of games down there for me I didn't perform as well, but I felt good with my stuff. I was happy to get the call and I'm looking forward to playing up here and helping these guys win."
The Astros have carried eight relief pitchers for most of the season, but they recently went to seven when they decided to carry six starting pitchers. After Lance McCullers couldn't pitch out of the first inning Monday, Mike Fiers -- Tuesday's scheduled starter -- threw five innings in relief.
"We needed an extra arm," Astros manager A.J. Hinch said. "It's his day to pitch in Triple-A and we wanted to get him up here and have an option in case we need him. We've beat up our bullpen a little bit the last week or so, mostly good situations, but they've all thrown a lot. We're not going to use Straily in the rotation moving forward."
Designating Straily for assignment was a procedural move involving option waivers.
"We may see him back up in September when rosters expand, or if we need him between now and then, obviously he's an option," Hinch said.
• Outfielder Preston Tucker, who left Tuesday' game with a bruised triceps after getting hit by a pitch, was held out of the starting lineup Wednesday but was available, Hinch said.
"Between today and yesterday, the mobility has gotten a lot better and swelling's gone down a lot, so hopefully tomorrow it will be good enough where I can go out and play," Tucker said.
• The Astros have brought back left-hander Joe Thatcher on a Minor League contract. He will report to Triple-A Fresno this weekend. Thatcher began the 2015 season with the Astros before being designated for assignment on July 21. Thatcher became a free agent after rejecting his outright assignment to the Minors.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.