Madison Bumgarner's return to the mound in San Francisco will have to wait.

Bumgarner, who is on the 10-day injured list with a mid-back strain, is scheduled to throw 70 pitches in a simulated game Sunday at Chase Field. He threw 46 pitches in a simulated game Monday and threw a bullpen session Thursday.

“He’s continuing to build up and get that pitch count up and get that moving in the right direction,” D-backs manager Torey Lovullo said. “I know that everybody wants to figure out what’s going to happen and when the next pieces will fall. I can't give you any more answers than that, because we've got to see how he feels after Sunday’s work.”

Bumgarner has missed two starts since going on the IL on Aug. 10, and he's missing this weekend's three-game series at Oracle Park, the D-backs' first trip to San Francisco this season. The former Giants ace lasted only two innings in his last start Aug. 9, allowing six runs on five hits (four homers) in a loss to the Padres.

“He's such a competitor,” Lovullo said. “I'm sure it would have been nice for him to come back into this stadium and pitch and get back on the mound that he was so familiar with, but if you were to ask me, I think he's turned the page and he wants to get here and compete for us and the Arizona Diamondbacks.”

Chafin gets splint
The D-backs are not sure when reliever Andrew Chafin, who was placed on the 10-day injured list with a left finger sprain prior to Wednesday night’s game against the A’s, will return to the mound.

The left-hander will have a splint on his left pointer finger for at least a week.

“Once the splint is removed at the end of the week, we'll get a better sense of how he's feeling and what the next steps are,” Lovullo said. “My conversations with him have been centered around keeping everything in shape. He's put himself in a good spot. His endurance has been built up. His legs are strong.”

Chafin has allowed six runs on nine hits in 6 2/3 innings this season, striking out 10 and walking four. Left-hander Matt Grace was recalled from Arizona's alternate training site to take Chafin's spot on the active roster.