Oakland center fielder Mark Kotsay will return to the Bay Area to get treatment for his injured back and is not expected to play until Friday. Kotsay missed six games with back spasms from Aug. 7-13. He has appeared in 17 of the Athletics' last 29 games. "The way he is now, there's no conceivable way he can play in the next few days," Oakland trainer Larry Davis said. "Now is not the time to be conservative. We have to be aggressive."