Machado, who had left knee surgery Oct. 14, had visited his Los Angeles-based surgeon Dr. Neal ElAttrache on Thursday and was given the go-ahead to resume all activities.
However, Showalter doesn't want to rush the 21-year-old All-Star, who injured his knee at Tampa Bay on Sept. 23.
"The thought of him starting the season on the active list is not realistic," Showalter said.
After Machado's surgery, a 4 to 6 month recovery was forecast.
Showalter said that he expected Machado to play again next month.
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