Borussia Dortmund celebrity Erling Haaland must still convince Lucien Favre of his match fitness despite a sensational start to life in Germany.

Haaland arrived in Signal Iduna Park from RB Salzburg last month, billed as one of the hottest properties in European football, and the teenage striker has certainly not disappointed.

The Norway international was at the double once more on his first start, with Union Berlin dismissed 5-0, although he was a replacement again for the DFB-Pokal tie at Werder Bremen in midweek.

Obviously, Haaland scored after his debut, although BVB dropped to a 3-2 defeat.

Asked whether he regretted not beginning the in-form ahead, Favre kept his sights trained on the bigger picture at a Thursday news conference.

“You don’t understand his fitness like I do. So, we must be careful. We need to be reasonable.

“Of course, I’d like to let him play all the games, but we still need to be cautious with him sometimes.

“He is 19 years old and I talk about pre-season and old injuries. We have to be reasonable.”

Favre’s hand might be forced, however, given his forward line will be without Marco Reus when they travel to face Bayer Leverkusen this weekend.

“Regrettably, Marco is injured now. It occurred at the last minute. I am very sorry for him,” said Favre, with his captain place to get a four-week spell on the sidelines due to a muscular criticism which will cause him to miss the Champions League showdown with Paris Saint-Germain on February 18.

“But Marco is still very important and will be important for the group. There are several options on how to replace him, but it is dependent upon the system. Now it’s still not determined.”

Emre Can, a deadline-day arrival on an initial loan from Juventus, made a substitute cameo against Werder and could make his league debut for Dortmund against old employers Leverkusen.

“We must see him in training, how he feels. He didn’t play a lot [in Juventus this season],” Favre added.

“He made a fantastic impression yesterday. The training was very long and intense. He did really well.

“He has to reveal in training what he is able to do. We know he can play as a defender with a back three but also in the midfield as six or eight, also in a 4-3-3.

“We will see because right now I cannot tell you exactly.”