Dunn could make his A's debut in time to help the club avoid a fifth consecutive defeat Monday against the visiting Seattle Mariners.
A loser in 14 of 20 and five games behind the Los Angeles Angels in the AL West, Oakland (78-58) still leads the majors averaging 4.7 runs despite scoring 3.6 per contest and hitting .223 while going 12-17 in August.
The AL wild card-leading A's were limited to 14 hits while being outscored 14-1 in the final three of a four-game sweep by the Angels. Oakland snapped a 29-inning scoreless drought with Josh Reddick's RBI single in the eighth of Sunday's 8-1 loss at Anaheim.
Oakland's slump has coincided with the trade of All-Star slugger Yoenis Cespedes to Boston for Jon Lester on July 31.
However, it's uncertain if the solution is Dunn, acquired from the Chicago White Sox on Sunday for minor league pitcher Nolan Sanburn.
''We're trying to do whatever we can to get some offense going here,'' manager Bob Melvin said. ''The guy has a history of hitting homers and getting on base, and I know he's excited about being with us.''
The 34-year-old Dunn has 460 home runs, 1,158 strikeouts and walked 1,311 times during his 14-year career. He's hit 20 of those homers and fanned 132 times while walking 65 in 106 games this season.
Dunn, whose 1,976 games played without reaching the postseason are the most of any active player, considers this to be his last shot at accomplishing that goal.
''This is probably going to be it,'' said Dunn, who plans to retire after this season. ''I've been playing a long time and haven't got this opportunity, so I'm going to try to make the most of it.''
Dunn struck out in both of his plate appearances against Chris Young (12-6, 3.17 ERA), who is 1-1 with a 2.50 ERA in three starts and also threw two scoreless innings of relief against Oakland this year.
Young won three straight starts, and allowed a run and six hits over 12 innings of the previous two, before giving up three runs, seven hits and five walks in 3 2-3 innings of a 7-3 victory at Boston on Aug. 23.
One-half game out of the final wild-card spot, Seattle (73-62) has won five of seven against the A's and took three of four at Oakland in May.
Dustin Ackley is 1 for 15 in his last five games versus Oakland, but is batting .370 with three home runs and 13 RBIs in his last 12 overall. He homered for the second straight game and matched a career high with four RBIs as Seattle snapped a three-game slide with a 5-3 win over Washington on Sunday.
"He believes in what he's doing," manager Lloyd McClendon said. "He's very confident in the type of player he is and it's showing up on the field.
Teammate Robinson Cano is batting .364 with two homers and 13 RBIs during a 21-game hitting streak against the A's. He's hit .387 with two doubles and a homer versus Jason Hammel (1-5, 5.77).
The right-hander posted a 9.53 ERA while losing his first four starts after Oakland acquired him from the Cubs in July, but is 1-1 with a 2.86 ERA in the last four - allowing one run twice and none another.
Hammel yielded a solo homer and two other hits in seven innings while not factoring in the decision of a 4-2 loss at Houston on Tuesday.