ST. LOUIS -- Cardinals third baseman Scott Rolen left Sunday's game against the Nationals in the eighth inning after a fourth-inning collision with Nats first baseman Dmitri Young at first base.

"He came out feeling fuzzy," manager Tony La Russa said. "He had the classic conditions or symptoms of a mild concussion. He said he's better. He isn't having trouble concentrating; he said he could drive home."

The play happened when Rolen grounded a ball to Nats third baseman Ryan Zimmerman. Rolen beat Zimmerman's throw to the bag, but collided with Young at first base. Young left the game early as well, with lower back pain.

La Russa said Rolen said he was OK to fly with the team to Denver on Sunday night for its four-game series against the Rockies. The team doctor didn't immediately say no to Rolen undertaking the trip.

"You have to be careful with those things," La Russa said. "I'm concerned about it. He felt good about it at the end of the game, though."

Rolen wasn't available after the game for comment. Head trainer Barry Weinberg said he wasn't sure of Rolen's condition.