Ortiz hasn't played since July 16 against the White Sox as he continues to recover from a right Achilles injury.
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"It only bothers him when he runs straight ahead," Valentine said.
Valentine said after Friday's game that a Sunday return for his DH was unlikely, but he didn't rule out the possibility on Saturday.
"I don't know," he said. "We're trying to make sure that he has no setback."
Ortiz is hitting .316 with 23 home runs and 58 RBIs in 89 games this season.