Journeyman right-hander Ross Wolf gets the call for the emergency start on Thursday night when the Texas Rangers visit Baltimore to wrap up a four-game series with the Orioles at Camden Yards.
The start had been scheduled for Japanese-born Texas strikeout ace Yu Darvish, but he was placed on the 15-day disabled list Wednesday with a mild strain in his upper back.
Darvish, who leads the majors with 157 strikeouts, will not participate in next week's All-Star Game in New York.
Wolf, a 30-year-old from Illinois, was an 18th-round pick of the Florida Marlins in 2002 but did not reach the majors until 2007 and was 0-1 in 14 relief appearances.
He had an 11-game stint with Oakland in 2010 and had made one start in 12 appearances with Texas, going 6 2/3 innings and allowing one unearned run in the lone start at Toronto on June 8.
He pitched one-third of an inning in relief against Baltimore on July 8, his lone career meeting with the Orioles.
Wolf is opposed by 29-year-old right-hander Miguel Gonzalez, who's won four of five decisions in his last six starts while trimming his ERA from 4.33 to 3.63.
He defeated the Cleveland Indians, 7-3, for his most recent victory on June 27 after giving up three runs on nine hits in 6 2/3 innings.
Gonzalez allowed just one run in six innings of a no-decision in New York against the Yankees on July 5, but the Orioles lost, 3-2.
In the last six starts combined, Gonzalez has given up 12 runs on 30 hits in 40 1/3 innings.
He's 0-1 in his career against the Rangers with a 7.20 ERA.
On Wednesday, Wei-Yin Chen spun seven stellar innings of one-run ball in his return from the disabled list, as the Orioles downed the Rangers, 6-1.
Chen (4-3) hadn't pitched for the O's since May 12 due to a strained right oblique muscle, but didn't miss a beat in his return to the mound, scattering three hits and three walks while striking out four.
Nolan Reimold clubbed a three-run home run and Manny Machado collected three hits, an RBI and a run scored for the Orioles, who had dropped back-to-back games to open this series.
"It's something to build on," Reimold said. "It was a good night and just enjoy it now and get ready for tomorrow."
The victory was Baltimore's 50th of the season, marking the first time the O's had at least 50 wins before the All-Star break since 1997 when they were 55-30.
Texas starter Josh Lindblom (1-3) labored through 5 1/3 frames, giving up all six runs on nine hits and four walks while tossing 119 pitches to absorb the loss.
A.J. Pierzynski recorded half of Texas' four hits, while Adrian Beltre knocked in the lone run for the Rangers, who had a three-game win streak halted.
The Rangers won five of seven games with the Orioles in 2012 and five of six between the teams in 2011. Baltimore last won the season series, 6-4, in 2010.