Flick acknowledged that his team wasn't up to scratch at Benito Villamarin stadium.
"We played very badly from the start," he added. "It wasn't a good game. We're a young team and we need to improve a lot. We need to be stronger, especially when we play away. We have quality, but we have to show it in every game.
"We were slow with our passes, with a lot of long balls... it's not what we want or our strength. We have to focus on our strengths and on what we have to do."