Arias was carted off the field and taken to the hospital after teammate Wandy Rodriguez inadvertently struck him in the head with a ball during pregame warmups. Assistant athletic trainer Rex Jones and several teammates rushed to Arias' side while he was lying on the outfield grass.
"It was really scary," Arias said after Friday's 9-1 win over the Pirates. "I didn't see the ball until it hit me. It just came right at me and hit right here [points to right side of forehead]. But I'll be fine, I feel better now."
Astros general manager Ed Wade said Arias might have been temporarily blinded by the sun because Minute Maid Park's retractable roof was open. Rodriguez didn't have an explanation.
"I was playing catch with him and he missed the ball," Rodriguez said. "I don't know what happened."
Arias spent about three minutes on the ground being checked out by team medical personnel before being driven off the field. He was taken to The Methodist Hospital for tests but returned to the ballpark in time for Friday's game.
Arias has a 3.97 ERA in 12 appearances this year.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.