Polanco is listed as day to day. While receiving treatment, he declined to comment on his injury following Saturday's game.
He sustained the injury while chasing Josh Donaldson's fly ball to shallow right field. Polanco couldn't get to it in time and came up limping, favoring his left leg, then exited the game with head athletic trainer Todd Tomczyk.
"Something grabbed him. That was it," bench coach/acting manager Tom Prince said. "That's why we took him out of the game. Precautionary, from what I've got right now."
The good news for the Pirates is McCutchen may be ready to return Sunday. The outfielder exited Friday's game with left patellofemoral discomfort, a knee injury that he did not believe to be serious. McCutchen did not play Saturday but said he went through a full pregame workout and felt good enough to contribute, if necessary.
"It felt fine. Show up tomorrow and hopefully be in the lineup," McCutchen said. "If they ever needed me, I was ready. Ready to go, but at the same time, don't need to be doing something and making it worse. Got to be safe."
The Pirates have tried to play it safe with Polanco, but injuries keep holding him back.
After an outstanding World Baseball Classic showing, Polanco was limited on Opening Day by a sore shoulder. He missed time in mid-April due to right groin discomfort. He was on the disabled list from May 15-25 with a strained left hamstring. He was carted off the field at PNC Park on May 29 with a sprained right ankle. He's played through an occasionally sore right knee.
For three weeks, Polanco was fully healthy and productive. He slashed .387/.406/.629 with three homers in 17 games from July 1-21, and the Pirates went 12-5 when he played during that stretch. Then came another trip to the disabled list due to a recurrence of his hamstring injury. He sat out from July 22-Aug. 2, and the Pirates went 2-7 during that stretch.
If Polanco is sidelined and McCutchen returns, the Pirates would likely turn to Adam Frazier and Sean Rodriguez to fill the hole in right field. Their other options include Jose Osuna and John Jaso, who moved to right field when Rodriguez entered to play left on Saturday.
The only other outfielder on Pittsburgh's 40-man roster is Jordan Luplow, who briefly made his Major League debut last month. The Bucs could reinforce their bench with another infielder, such as Max Moroff, given the versatility of Rodriguez and Frazier.
Polanco is slashing .255/.311/.407 with 10 home runs, 32 RBIs and eight steals this year.
"It sucks. Trying to keep him healthy but need to be safe about the whole situation, him needing to be healed," McCutchen said. "We don't need him to be 80-85 percent right now. A hamstring's a difficult thing. You don't want that happening to a 25-year-old. He needs to be healthy. I don't know everything that's going on there. We just need him healthy. We don't need him 80 percent."