Jockey Patrick Valenzuela has been named to ride four horses on Thursday's card at Oak Tree at Santa Anita, but may not know whether he'll be allowed to ride until a few hours prior to post time.Valenzuela, who had reportedly been battling a back injury and was briefly hospitalized for undisclosed reasons this past summer, was required to submit medical documents to the California Horse Racing Board detailing his recent absence. According to his agent, Tom Knust, Valenzuela presented the required papers on Monday and is hopeful they will satisfy the board."They're allowing us to be named on horses for Thursday," Knust said prior to entries being released. "We're working together (with the CHRB) to get this resolved. They received the documents and we believe they'll be satisfactory."CHRB chairman Richard Shapiro would only say, "We have tentatively agreed to let Patrick Valenzuela accept mounts for Thursday subject to the resolution of one issue, which we hope to resolve before Thursday."Valenzuela, who has been in and out of the saddle due to substance abuse problems, has not ridden in California since the final day of the Hollywood Park spring-summer meeting on July 16. The 43-year-old jockey was scheduled to ride on the opening day card at Del Mar July 19, but took off citing a sore back. He was then briefly hospitalized in August for undisclosed reasons and though he reportedly passed several drug tests, was also unavailable several times when CHRB investigators went to his house.He was given clearance by Del Mar stewards to resume exercising horses earlier this month, though the CHRB refused to allow him to ride until he submitted satisfactory medical information. In his only mount since July, Valenzuela won the Woodbine Mile (gr. IT) aboard Team Valor's Becrux after Canadian officials were told by the CHRB that there were no official rulings pending against him.Since 2001, Valenzuela has ridden in California on a provisional license, which has been amended several times to include stricter conditions. According to Knust, Valenzuela has passed several urine and hair shaft drug tests this month.