Pitchers Jonathan Loaisiga, Nestor Cortes Jr. and Wandy Peralta all tested positive, Yankees General Manager Brian Cashman told reporters.
Three other tests were pending, said Cashman, who assumed all would come back positive.
This came after ESPN's Buster Onley reported that three Yankees position players were placed in COVID-19 protocol: Aaron Judge, Kyle Higashioka, and Gio Urshela.
Because Judge was at the All-Star Game in Colorado, Red Sox players (and presumably others) were also undergoing contact tracing along with the Yankees, he said.
The grudge match between the two AL East rivals was to begin a critical four-game series for the Bronx Bombers and was the only scheduled game kicking off MLB's second half.
The Yankees scrapped batting practice, however, and asked reporters gathered on the field to leave "for their own safety" following two reported positive tests involving pitchers Cortes and Peralta. Both had been placed on the COVID-19 injured list before the game because of health and safety protocols.
"There may well be more players as well as staff," Onley said. "There is more testing that has to happen tomorrow [Friday]."
That would determine whether baseball would be played at Yankee Stadium on Friday, he said.
Ken Rosenthal broke the news on The Athletic.
Major League Baseball confirmed the report moments later: “Following positive COVID-19 tests within the New York Yankees organization, tonight’s game between the Yankees and the Boston Red Sox at Yankee Stadium has been postponed to allow for continued testing and contact tracing. Major League Baseball will continue to provide scheduling updates as available.”
First-place Boston (55-36) and New York (46-43), tied for third in the division with Toronto, had eight games in all scheduled over the next 11 days. Thursday night's game was supposed to air on national TV.
Red Sox prospect Jarren Duran also had been scheduled to make his major league debut in centerfield and batting seventh.
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