"It's nothing bad," Polanco said. "No DL situation or anything. It's probably day to day."
Polanco limped off the mound before he dropped to the turf. Two team athletic trainers helped Polanco off the field and into the visitors' clubhouse down the left-field line at McKechnie Field.
"When it first happens, you really get scared," Polanco said. "You don't know what's happening. It doesn't feel right. But now that the doctor took a look at it, it's nothing big at all. ... It's getting better now already after the icing and all that."
A Pirates doctor checked Polanco's knee ligaments. Polanco said he does not think an MRI exam is necessary.
"It's just the back of the knee," Polanco said. "It's probably hyperextended a little bit -- irritated."
Polanco tried to catch Delwyn Young's popup in the third, but he lost the ball in the sun and stumbled on the back of the mound.
"Tomorrow is a big day to see how it feels, how sore it is," Polanco said. "Probably two or three days, because we've got a day off coming [Thursday]."
The Phillies signed Polanco to a three-year, $18 million contract in the offseason to replace Pedro Feliz at third base. Polanco is trying to get acclimated to playing third again after playing second base with the Tigers from 2005-09.
Phillies manager Charlie Manuel was asked if his heart jumped in his throat when he saw Polanco get hurt.
"I hope it don't," Manuel said. "I'll be in trouble if it does. When I see something like that, yeah, I'm very concerned, because Polly is one of our main players. ... He can play. He can hit. He can field. He can throw. He's an All-Star."
Todd Zolecki is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.