Zito went into the All-Star break with a 4-7 record and 4.62 ERA, making him 10-13 since the 2003 break.
The 2002 AL Cy Young award winner is 0-4 in six starts since beating Cincinnati on June 8.
“I’m frustrated with myself,” Zito said after a 4-1 loss to Cleveland on Sunday. “I’ve got to get better. I’ve got to make better pitches.”
Zito will try to match teammate Rich Harden’s effort as the A’s go for their third straight win.
Harden pitched eight innings of four-hit ball to lead Oakland to a 4-2 victory over Chicago on Thursday. It was the first win in six starts since June 9 for Harden.
Eric Chavez hit his 14th home run for the A’s, who snapped Chicago’s four-game winning streak with just their second victory in seven games.
Chavez missed 33 games with a broken right hand before returning last weekend in Cleveland. He has hit safely in all four games since coming back.
Magglio Ordonez hit a two-run homer in the seventh for the White Sox, who stayed in first place in the AL Central thanks to Minnesota’s loss to Kansas City.
Chicago has lost all three meetings with Oakland this season.
Buehrle will try to end that trend Friday. The left-hander has won eight of his last nine decisions, and is 3-0 with a 2.98 ERA in eight road outings.