Tom Seaver, a key player from the 1969 “Miracle” New York Mets World Series team and member of baseball's Hall of Fame, is battling a serious health issue, according to a former teammate whose nostalgic new book about their championship season is nearing release.

Art Shamsky, who hit .300 with 14 home runs that season for the Mets, details some of the health issues of other teammates as well, among other things, in “After the Miracle,” Newsday reported this week.

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Shamsky, 77, wrote that Seaver suffers from short-term memory loss that could stem from Lyme disease. Seaver, 74, apparently told Shamsky he contracted the disease in 1991 when he lived in Connecticut.

Bud Harrelson, another key player on the championship team, which defeated the Baltimore Orioles in the World Series, four games to one, had reportedly been making visits to Seaver regularly and told some members of the team to be prepared when they re-connected with the three-time Cy Young award winner.

“He can forget things that happened just a few minutes before,” Harrelson told Shamsky, according to Newsday. “And he repeats himself a lot. But when he gets his rest, he still has a lot of energy.”

Harrelson, 74, is having his own health struggles. The former Mets shortstop was diagnosed with Alzheimer’s disease in 2016. He opened up to CBS New York last year and told the station he immediately stopped driving.

Shamsky wrote in his book that a few of “Miracle” Mets did go and visit Seaver, despite the pitcher’s wife saying that he has good days and bad days, according to Newsday.

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Still, Shamsky wrote: “He remains a larger-than-life figure — even to his teammates, and on this day he was as gregarious as ever, with a booming voice that filled the house. It was clear to me that he was enjoying one of his ‘good days.’”