The Argentine defender, who has played more than 840 games for Inter, had an operation on his ruptured Achilles at the end of April and was told he faced six months on the sidelines.
"We talked at length about the injury and we decided to do another year together," Zanetti told the club website on Wednesday. "They have shown once again their belief in me and my passion for Inter.
"I hope I can repay them on the pitch for this gesture of affection and esteem."
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