Manager Terry Francona said Beckett has inflammation in his elbow and likely won't start again until next Friday, when the Red Sox return home to open a three-game series against the Chicago White Sox.
Beckett, who took Thursday off, threw in the outfield for the second straight day Saturday and won't throw off a mound until Tuesday. He said the decision to push his start back was made after he felt numbness and tingling in his hand again Friday.
"It's gotten better," he said. "We had the one day [Friday] where it kind of came back. That's why we decided to do what we did. It has gotten better. The treatment and stuff is definitely working."
Francona intends to be "overly cautious" with Beckett, who is 11-9 with a 4.34 ERA in 23 starts.
"We're talking about a guy's pitching arm," Francona said. "Let's make sure it's perfect."
Beckett first reported numbness and tingling in his right hand after sleeping on his arm the night before his latest start, Aug. 17, when he gave up eight runs and eight hits in 2 1-3 innings in a 15-4 loss to Toronto. He's now sleeping with a special sleeve to prevent a recurrence of the problem.
"It's like a cast," Beckett said. "So we're dealing with that, too. The doctors say it's going to help, so we're going with it."
Concerned that taking Thursday off may have contributed to the numbness returning, Beckett intends to do light throwing every day.
"I think that was part of the problem yesterday, having that whole day off and not doing any treatments," he said.
Beckett didn't mind not pitching in what could be Boston's final visit to Yankee Stadium.
"There's a last time for everything," he said. "This didn't happen to be it."