The Reds took an early lead in Cologne thanks to a penalty from Bruno Fernandes, but the Spaniards hit back with goals from Suso and Luuk de Jong, either side of a deluge of United chances while the game was locked at 1-1.
The skipper was adamant that Ole Gunnar Solskjaer’s team were the better side on the night, but added that a lack of composure at both ends of the field had let the side down.
“It's difficult [to take]. The boys are devastated in there,” Maguire told BT Sport. “We created numerous amounts of chances.