Red Sox manager Terrry Francona also indicated on Saturday that Beckett is dealing with "inflammation" in his right elbow and that the earliest he could return is next Friday's series opener against the White Sox.
Right-handed starter Tim Wakefield, who has been sidelined since Aug. 7 with tightness behind his right shoulder, threw a side session on Saturday and was pronounced ready to return from the disabled list. He will be activated from the 15-day DL on Tuesday to pitch against New York in place of Beckett.
Beckett played catch on Friday and, according to Francona, initially felt fine. The right-hander was then slated to throw from the mound in a side session on Saturday. However, when the numbness began to creep up on him following Friday's activity, the Red Sox decided to change Beckett's throwing schedule.
Beckett instead played some light catch on Saturday, but will not throw in a side session until Tuesday.
"It's gotten better," Beckett said of the numbness. "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 did not want to take any chances with Beckett, who has gone 11-9 with a 4.34 ERA in 23 starts this year.
"The more we thought about it, we were thinking that we're trying to do everything in our power to make sure this guy's able to go out and pitch like he can pitch," Francona said of Beckett.
"I just think we all feel a little bit better about it [this way]," Francona added later. "We're probably being overly cautious, but when it comes to somebody's arm and their future, I just think we need to do that."
Beckett agreed with the manager's thinking.
"I think we're just going at this the right way," said Beckett. "I'm in support of it. It's the right thing to do."
Beckett had originally felt some numbness in the pinkie and ring finger of his right hand during his last start, against the Blue Jays, on Aug. 7. In that outing, he allowed eight runs on eight hits over just 2 1/3 innings.
"My hand and my fingers were really concerning me," he explained on Saturday. "Obviously, coming from the elbow. It's very minimal pain, it's just an uncomfortable feeling, not being able to feel a couple of your fingers."
Beckett initially thought the injury could have been caused by sleeping on his right arm. Recently, he has been given a special sleeve to wear while he is sleeping, in order to prevent any similar occurrences.
"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."
David Singh is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.