"He told everybody to enjoy our off-day and that when we got back, the schedule would be the same," Cook said.
What Cook didn't know at the moment was that he wouldn't be back and that his schedule wouldn't be the same.
"Then he told [us] that [we] might want to turn the TV on tomorrow night, check it out and watch the D-backs game, because [we] might get to watch one of [our] teammates pitch," Cook said.
"Everyone kind of lost it on the bus."
Cook, a 24-year-old right-handed reliever, was called up on Wednesday along with reliever Bryan Shaw, while the D-backs outrighted reliever Yhency Brazoban and optioned starter Barry Enright to Triple-A Reno.
"It was a shock to me," Cook said. "I was just going about my business and the next thing you know, I got the call."
In Mobile, Cook took over the closer's duties after Shaw was promoted to Reno earlier this year.
He had a 2.25 ERA with 50 strikeouts in 44 innings for Mobile.
D-backs manager Kirk Gibson said he would probably slot Cook into a fifth-through-seventh-inning role.
"He's been evaluated from everybody in the organization throughout the year, and I think they feel that he's got the kind of stuff that can help us," Gibson said.
He noted that both moves were made after the bullpen was heavily taxed in Tuesday night's 11-3 loss to the Brewers.
"We wanted to have our bullpen recharged," Gibson said. "We didn't want to be short down there."
Anthony Fenech is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.