Sandberg told reporters in Philadelphia Tuesday that he lost six pounds in two days.
"A couple of coaches took a bite and didn't like what they saw and threw the rest away," Sandberg said. "I was in a rush, so I ended up putting it away. I had one piece of toast in two days, and I'm feeling fine about that. I don't want anything in my stomach.''
Duda was hospitalized and missed Friday's game against the Phillies with a stomach ailment. He said Tuesday at Yankee Stadium that he, too, believes a Shake Shack burger was the culprit.
"I think it was undercooked," Duda said, according to ESPN.com.
The popular burger chain has a location in left field at Citi Field.
The Mets and Phillies played a three-game series Friday, Saturday and Sunday. Philadelphia won two of three.
A Shake Shack spokesman said Tuesday the company learned of Sandberg's accusation through Twitter on Tuesday and was trying to get in touch with the Hall of Famer.
"At this point we have no further knowledge of the situation, and there have been no other related reports whatsoever," spokesman Greg Waters said in a statement. "Food safety is of paramount importance to us, and we're connecting with our management team at the Citi Field Shake Shack now to discuss further and find out more."
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