Beltran was set to play right field Friday night against San Francisco. The Cardinals hold a 3-1 lead in the series.
The All-Star outfielder did not play Thursday night, a day after he left after one inning because of a strained left knee.
The 35-year-old Beltran is hitting .400 with three home runs, five doubles and six RBIs in 30 at-bats this postseason.
Beltran said he got acupuncture and a needle in his knee, went through 4½ hours of treatment and ran sprints earlier Friday.
Beltran said it was up to Cardinals manager Mike Matheny to make the call on whether he would play.
"Mike's concern was if I'm able to play the outfield," Beltran said. "I needed to go out and make some sprints 100 percent and if I don't feel anything, there's no reason not to say I'm ready to go.
"I'm ready to go."
Information from The Associated Press was used in this report.