An internet video showed Valverde putting his glove, with the ball in it, to his mouth before delivering a 1-2 pitch to Reds catcher Devin Mesoraco. Mesoraco swung and missed at the 94-mile per hour fastball.
"It's nothing. I never did anything wrong," Valverde said on Tuesday before the Tigers opened a series at Wrigley Field. "I put my glove on my mouth, yeah. Why? Because I sweat too much. That's it."
"Everybody can say whatever they want to, but I wasn't doing anything wrong because I've never spit on the baseball. Everybody said what I was doing, but when you play in a stadium like that, Cincinnati is so hot. I sweat too much."
He said he saw the video and anticipated the media's reaction, laughing as a group of reporters approached him in the clubhouse.
Valverde is 3-1 with 12 saves in 15 chances. He has a 3.91 ERA.
He said he has not been contacted by Major League Baseball.
"When they want to talk, I'll be here all the time," he said.