Ryan Dempster, who was slated to start Saturday's meeting against the Blue Jays, will miss the second game of the weekend series because of personal reasons and was placed on the restricted list.
In his place, the Rangers are turning to veteran righty Roy Oswalt. He hasn't made a start since July 30, when he was roughed up by the Angels for eight runs in 5 1/3 innings of work on 11 hits, three of which were home runs.
His next two appearances out of the bullpen were better, as he did not allow a run in four innings, but the Red Sox tagged him for four runs on three hits and a walk in his most recent appearance.
"It's a little different than what I'm [used] to -- usually I start every five days," Oswalt said. "Just sitting down there [in the bullpen] waiting on a phone call."
Carlos Villanueva takes the mound opposite Oswalt for the Blue Jays and is looking to pick up his first win in four starts. Last time out, he received a no-decision against the White Sox, going seven innings and allowing just one run on five hits and a walk to go along with eight strikeouts.
Villanueva has fared well in his transition from the bullpen to the rotation, winning four of his first five starts before losing the next pair. He has a 6-2 mark on the year with a 3.12 ERA.
Rangers: Hamilton rebounds after rough June and July
Though he had a rough 0-for-4 night Friday, slugger Josh Hamilton has found his swing in August after a rough two months.
Hamilton slumped in June, hitting just .223 with four homers, and followed it up with an even worse July in which he batted .177 with four dingers and 11 RBIs.
But the woes left Hamilton once the calendar turned again, with the 31-year-old hitting .308 with five home runs and 17 RBIs. His most recent blasts came Wednesday, when he hit two for his third multihomer game of the season, and the outing tied him with Adam Dunn for the Major League lead.
Hamilton is likely looking forward to facing Villanueva once again after knocking four hits in five at-bats against him all time, including a homer and a triple.
Blue Jays: Disabled list looks to become less crowded
Toronto is hoping to gain another player off the disabled list in the next week with the return of righty Brandon Morrow, who could be back with the club next Friday or Saturday.
Morrow is scheduled to make one more rehab start with Double-A New Hampshire on Sunday before rejoining the Blue Jays.
The team opens a weekend series at Baltimore starting that Friday, and manager John Farrell said he would stay with a five-man rotation.
"We've got some flexibility with this next turn through the rotation, particularly with Monday being an off-day," Farrell said. "So it's not been set in stone yet. But we've got to get through Sunday first to really outline the first two series of the trip."
Morrow is 7-4 with a 3.01 ERA on the season.
Right fielder Jose Bautista is scheduled to take batting practice Saturday after taking a day off from hitting drills Friday.
Third baseman Brett Lawrie is set to begin his rehab assignment with Class A Dunedin over the weekend.
Rangers hitters have collectively batted .267 against Villanueva in their careers, but the only player with a homer off him is Hamilton.
Edwin Encarnacion leads Toronto in hits, homers, RBIs and walks, the only player in the American League to lead their team in all of those categories. If he finishes the season with the team lead in each category, he would be just the third Blue Jays player to do so.