Bayern Munich coach Pep Guardiola hailed the impact Douglas Costa has had since arriving at the club from Shakhtar Donetsk.
Costa played 90 minutes in Bayern's 1-0 win over Real Madrid on Wednesday that saw Guardiola's men secure the Audi Cup at the Allianz Arena, with the Brazil international starting on the left wing in a 4-3-3 formation.
The 24-year-old has started all but one of five friendlies this close-season, while he also played the entire 90 minutes in Bayern's DFL-Supercup loss to Wolfsburg on Saturday.
But when Costa signed a five-year deal on July 1, there was plenty of criticism from the German media and Bayern fans, according to Guardiola, who is convinced the Brazilian winger will help some of his star players improve.
"I thought that something like this would happen," Guardiola said.
"Bayern have signed a player. A player that not many people knew about because he played for Shakhtar. At first, the media criticised the transfer but the club gave him time. People criticised Douglas Costa without knowing him.
"I have to admit I was surprised a bit too. I knew his qualities because I played five or six times against Shakhtar. And I knew his qualities were in the one-on-one. But it is not only that, he can play both left and right and also works defensively.
"From the first moment on, we saw what a great player he is. Bayern Munich is lucky to have him. He is a young player and he has a lot of potential. He is great when it is one against one, or against two or three.
"Robert Lewandowski will play better because of him, Thomas Muller will, Franck Ribery and Arjen Robben will also."
In six seasons with Shakhtar, Costa scored 29 goals and notched 30 assists in 141 league matches.
