When the Dodgers optioned Withrow to Triple-A Albuquerque on May 21, Mattingly said it had nothing to do with his performance.
"We got caught in a bit of a numbers game," Mattingly said.
Withrow, 26, was the only reliever who still had an option; the others are vested veterans with difficult-to-trade contracts and they can become free agents if taken off the Major League roster. Withrow had a 2.95 ERA in 20 appearances for the Dodgers, after going 3-0 with a 2.60 ERA in 26 games as a rookie last year. When left-handed starter Hyun-Jin Ryu came off the disabled list, Withrow was the only pitcher the Dodgers could move without losing.
"He pitched the night before [the option]; he was throwing 95 [mph]," Mattingly said.
Withrow, who was not at Dodger Stadium before Thursday's series opener with the Pirates, went to see trainer Stan Conte last week before joining the Triple-A Albuquerque Isotopes because he was having elbow discomfort. The Dodgers had put him on the Major League DL Saturday, although nothing was announced until Thursday.
"I didn't know until yesterday that there was nothing out there about it," Mattingly said, when asked about the delayed announcement. "Stan told me in New York that there was something bothering him, and that we were going to send him to L.A.
"There's nothing secret about it. We already sent him down, then we put him on the DL. We didn't mistreat him, or gain any advantage from it [lack of an announcement]."
Opponents hit .143 against Withrow this year. He had 28 strikeouts in 21 1/3 innings.