Borussia Dortmund chief Hans-Joachim Watzke has defended the sale of Erling Haaland to Manchester City.

Haaland has left the Bundesliga side in favour of reigning Premier League champions City.

The 21-year-old underwent medical tests in Brussels on Monday afternoon before the £51m deal was completed on Tuesday afternoon.

Watzke told CNN: "That's the only way for us because when a player performs very well, we have to fight against the big, big, big clubs with the oligarchs and the Arabian states at their back.

"And this fight we cannot win, but we can win a fight over an 18-year-old player, like Jude Bellingham, because this player loves to play at Borussia Dortmund because we have always 80,000 spectators, it's a very good atmosphere and the club knows how to manage young players.

"That's our way and, okay, we have a good department who are scouting young players every day, but it's also very important if you have the player here, you must develop him and I think that works ... most of the time, it works."

The 62-year-old also insisted the Bundesliga side will survive without the Norwegian as they overcame the departures of former stars Robert Lewandowski and Pierre-Emerick Aubameyang.

"It's a decision for Erling," Watzke said. "Erling, you know, has an exit clause and he must decide if we wants to take this exit clause or not and he has time to give us his decision. When the time is ready, he will do it.

"But we [Dortmund] have played football for 113 years, and for 111 years, we played without Erling Haaland. We had Robert Lewandowski and then he left us in 2014, but we played football in '15, '16, '17 until now.

"Then next came Pierre-Emerick Aubameyang and then Erling Haaland and you can be sure if Erling takes a decision to leave us, we will find the next [player] 100 per cent."