Gonzalez slipped below .500 for the year in his last start on Wednesday in Toronto, as he allowed four runs and four hits and walked five batters over five innings to fall to 9-10 on the year to go along with a 3.25 ERA.
"Good pitchers go through difficult times," Oakland manager Bob Melvin said. "This isn't the best time of the season for him. He's going to have to work his way through it, and he will."
The All-Star left-hander lost to the Orioles earlier in the year and is 1-1 in four starts against them with a 2.59 ERA.
Oakland could use a big start from Gonzalez this evening after it was swept in a three-game set by the Texas Rangers over the weekend. The A's rallied from a six-run deficit on Sunday, before falling, 7-6.
"It's a tough one to lose. Especially since we came back," Oakland's starting pitcher Rich Harden said.
Baltimore, meanwhile, avoided a sweep on Sunday, as Nick Markakis went 3-for-5 with a home run and four RBI to power the Orioles past the Detroit Tigers, 8-5. Nolan Reimold doubled twice and scored three runs, and Vladimir Guerrero knocked in a pair of runs for Baltimore, which picked up just its second win in eight tries.
Jo-Jo Reyes (6-9) earned the win after holding the Tigers to one run on four hits in six innings. It was his first victory in two appearances since the Orioles claimed him off waivers from Toronto on August 2.
"It was good to see him pitch well," said Orioles manager Buck Showalter.
Tonight, the O's turn to another newly acquired hurler in left-hander Tommy Hunter, who is 1-2 with a 4.67 ERA. Hunter, picked up from Texas as part of the Koji Uehara deal, did not factor in the decision of his team's 6-4 win on Wednesday against Chicago, but allowed four runs and seven hits in 6 2/3 innings.
He is 4-0 in seven games (five starts) against the A's with a 4.59 ERA.
Oakland has split its six games with the O's this season after winning seven of the 10 matchups in the season series a year ago.