BALTIMORE — Josh Beckett's next start has been pushed back a few days while the Boston Red Sox try to determine the cause of lingering numbness in the his right hand.

"We've got to figure out what ... it is," Beckett said Tuesday. "Obviously, (being pushed back) is not what I want, but at this juncture it needs to happen."

Beckett was scheduled to pitch Saturday against Toronto. Instead, he's tentatively set to start Tuesday night when the Red Sox play New York at Yankee Stadium.

"I don't know. It's still seven days away," he said. "We'll see."

Beckett will undergo tests to determine the cause of the numbness — and to rule out a serious condition such as a blood clots.

"That's what we're trying to stay away from. Anytime there's something wrong with your arm, a baseball player, especially a pitcher, you think of the worst first. I've been kind of reassured by people that it's not that," he said.

Beckett slept wrong on his right arm the night before his last start Sunday against Toronto. He then lasted only 2 1-3 innings, giving up eight runs and eight hits.

"He slept on his arm the other night and he came in and felt some tingling in his fingertips," Red Sox manager Terry Francona said. "I think it didn't help his location."

Beckett said he has intermittently dealt with the problem this season, but not to the extent that he felt the numbness Sunday.

"As far as pain goes, it's not that much pain at all with it. ... It's something we've monitored over time. It hasn't ever festered until now," Beckett said.

Left-hander Jon Lester will take Beckett's start Saturday. Beckett has scheduled days off Wednesday and Monday, and Francona wants to keep the ace on his regular program between outings.

The Red Sox lead the AL wild-card race. Boston plays a three-game series at Yankee Stadium next week, its final regular-season visit to the ballpark.

Meanwhile, outfielder J.D. Drew's balky lower back is progressing, but he was out of the starting lineup against Baltimore for a second straight game Tuesday.

"Improved — not ready to play, but he's improving," Francona said.