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Szczesny made eight saves for Barcelona in its 1-0 win over Benfica in the first leg of the Round of 16, a huge result after Pau Cubarsi's 22nd-minute red card.

Benfica had 26 shots against Barcelona, its most on record since 2003-2004 in a UEFA Champions League match without scoring, which was all down to Szczesny's display.

The 34-year-old has become a mainstay in Flick's team since coming out of retirement last October to cover for Marc-Andre ter Stegen's season-ending injury.

Szczesny has kept eight clean sheets in his 14 appearances across all competitions this season, conceding just 13 times, with Flick happy with his performances thus far.

"He is fantastic. The other players were defending 10 against 11, and he helped us a lot. That is his job. We cannot hide it," Flick said.

"He does his job very well, and that is why he is now the number one.

"When you watch players in training, you get a feeling. I discuss it with my staff. I see how the players work and what level they can reach.

"It was clear to everyone that Szczesny could reach this level. We all knew it. I make the decisions, but I talk with my coaching staff."

Barcelona now turn its attention back to LaLiga, with 11th-placed Osasuna the next visitor to Estadi Lluis Companys this weekend.

Flick's side is one point clear at the top of the table, but the Barcelona boss is wary of Osasuna, which inflicted the Blaugrana's first loss of the season in September.

Osasuna was a 4-2 victor in the reverse fixture, having lost each of its previous five games against Barca.

Barcelona, however, has never lost both matches in the same campaign against Osasuna in LaLiga.

"It was different, we played away. Tomorrow, we have to field the best possible team. I think our performance level is different now. I am optimistic about tomorrow's match," Flick said.

Barcelona has won each of its past six LaLiga matches, keeping four clean sheets, having won just one of its previous eight in the competition.

It is also the first team to score 71 or more goals in its first 26 games of a LaLiga campaign since it did so in 2016-2017, when it scored 76 goals.

"It is always good to be positive and to maintain a positive image at all times. If you approach things from a negative perspective, trying to avoid mistakes, I don’t think that’s good. We can defend well as a team," Flick concluded.

"It will be a tough game. I always say the same. They played very well there, pressed us well, also in one-on-one situations. It was difficult for us to get out of their press. We will try to be prepared."