"We scouted him extensively and obviously engaged with his agents," Cashman said. "We made our final and best [offer] yesterday and we were told that it wasn't going to be good enough. Obviously we were waiting to hear where he was going to be going. It sounds like he's going to Boston."
The Yankees were viewed by many as the front-runners to land Moncada, who would have been a cherry on top of a spending spree that has totaled more than $15 million in the international signing market since last July, severely limiting their bonus pool expenditures for the next two years.
Moncada worked out three times for Yankees evaluators in Tampa, including twice last week, and was being talked about as a future big league second baseman or third baseman.
"I don't think anybody disagrees with the ability," Cashman said. "I would doubt there's any disagreement on the scouting assessment of the player. It just comes down to how much money you're willing to commit. As I said, we put our best foot forward yesterday. It was a significant offer, but it fell short of where he's rumored to have signed."
A 100 percent penalty on the bonus played into the Yanks' hesitation to push past $25 million, though the New York Post reported that the club was willing to go as high as $27 million for Moncada. Because of that tax, Boston's investment in Moncada will be approximately $63 million.
"I think it was a significant issue for a lot of people, including ourselves," Cashman said. "I'm sure even the Red Sox were a part of it. It's definitely a hurdle to deal with."
Cashman said that when the Yankees presented their offer to Moncada's representatives on Sunday, he did not have confidence that the prospect would wind up in pinstripes.
"You knew it was going to be aggressive," Cashman said. "It felt like two teams at the very least were obviously battling it out, and one of those two teams was obviously Boston. And Boston, it looks like, secured him."
Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch and read his MLBlog, Bombers Beat. This story was not subject to the approval of Major League Baseball or its clubs.