Cincinnati acquired Lamb and fellow lefty prospects Brandon Finnegan and Cody Reed from the Royals in a trade for Johnny Cueto on July 26.
"I think it's something that John earned, really, the way he was pitching with Kansas City when we got him," Reds manager Bryan Price said. "He's thrown the ball well for our Triple-A club. It's going to be unusual for him I'm sure. There's a newness to our organization, then he goes to Triple-A and makes a few starts and all of a sudden, he's in the big leagues with people he doesn't know. We're excited to have him in the organization and to be able to provide him a well-earned opportunity for him to make his debut on Friday."
The No. 21 prospect in the organization, according to MLB.com, Lamb has gone 10-2 with a 2.67 ERA in 20 Triple-A starts this season for Omaha and Louisville. In 111 1/3 innings, he has allowed 94 hits, 36 walks and has 117 strikeouts.
When he pitches, Lamb will wear Cueto's old No. 47 and be the seventh different Reds player to make his Major League debut this season -- and the sixth starting pitcher.
Lorenzen gave up seven earned runs and seven hits over 1 1/3 innings in his latest loss, an 11-6 defeat to the Padres on Tuesday. Since his last victory on June 21, he was 0-6 with an 8.49 ERA, including a 12.57 ERA in five second-half starts.
"Just to get the repetition that he needs to get back on top of his game and I'm sure we'll transition him to the bullpen," Price said of Lorenzen. "It's realistic to have him with us in September. I think it's important to have him pitch in September."
With a 3-8 record and 5.46 ERA in 19 games, including 17 starts, Lorenzen has struggled with his fastball command in recent outings. During a Wednesday night meeting at the team hotel, he and his agent, Scott Boras, went over his pitching issues. Lorenzen said Boras told him his struggles traced back to mental-approach issues.
"I didn't believe it was a mental issue. I thought it has to be mechanics," Lorenzen said before departing Dodger Stadium. "I guess it's the way I think. But we broke it down. I threw my bullpen today and everything was back to normal. I mean it felt really good. Now I'm a firm believer that it was mental. I'll go down to Triple-A, just apply it and get back up here."
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.