FC Barcelona will have to “make the impossible possible” on Tuesday as they attempt to overturn a four-goal deficit against Atletico Madrid in their Copa del Rey semi-final, head coach Hansi Flick said.

Atletico stunned Barcelona in last month’s first leg, racing into a four-goal lead before half-time and inflicting the Catalans’ first scoreless domestic outing of the season.

Despite the daunting task, LaLiga leaders Barcelona have not given up hope of defending their Copa del Rey crown. Speaking to reporters on Monday, Flick insisted belief would be key to any comeback.

“We are four goals behind, and we have to make the impossible possible. That is the objective. It’s not easy. However, we will not give up,” he said.

“It is important to keep a clean sheet, but we must believe in our strength and that we can achieve it. You must always believe. For example, in each half we need to score two goals.”

Barcelona’s attacking form offers some encouragement. The Catalans lead LaLiga’s scoring charts with 71 goals this season and have struck seven times across their last two matches, including a hat-trick from teenage star Lamine Yamal in Saturday’s win over Villarreal.

However, Flick must cope without veteran striker Robert Lewandowski, who fractured his eye socket in that game and will miss the decisive clash.

“We will have to manage Lewy’s absence. We have not had much luck. Losing a player like him, and the others who cannot be there, is a problem, but the team handles it well,” Flick said.

The German coach also stressed the importance of discipline against an Atletico side renowned for their threat on the counter-attack.

“We must press them, win the duels and make things difficult for them. We cannot lose possession, as they are very dangerous in transition. We have to play as one, especially tomorrow.”

Barcelona now face a monumental challenge at home, knowing only a near-perfect performance will keep their hopes of silverware alive.