In the final match of the UEFA Nations League group stage, La Roja completely dominated their opponents, recording 23 shots to two - 10 on target compared to zero - while they also finished the game with 70 percent possession.
"If I look back at my career, it was perhaps not the most bitter defeat, like the Champions League final in 2012 [with Bayern Munich against Chelsea], but it was the clearest," Kroos said on his and his brother Felix's podcast, 'Einfach mal Luppen'.
"Never in a defeat have I felt so powerless.
"We did things really badly and we have to analyse what went wrong. Three months earlier we had played against Spain with almost the same team; it was 1-1 and we should have won.
"Now there will be a long phase without international matches which is annoying, but we must see it as an opportunity. We will improve, we have already shown that we are capable of it."