Haaland is in much demand from some of Europe’s biggest clubs, having starred for Dortmund since arriving from RB Salzburg in January 2020.
The 20-year-old is the top scorer in the Champions League this season with 10 goals while his 21 appearances in the Bundesliga has yielded 21 goals.
Haaland has been tipped to leave Dortmund sooner rather than later, especially with the Black and Yellows in danger of missing out on Champions League football next season.
But Sammer believes despite Haaland’s impressive numbers in front of goal, he is not yet the finished article and he has urged the Norwegian international to use the contrasting fortunes of Robert Lewandowski and Ousmane Dembele as examples after they left Dortmund.
“I would recommend for Erling to also see the value of Borussia Dortmund,” Sammer, who now serves as one of Dortmund's technical advisors, told Sport Bild.
“The club has given him a lot. From here, he can only go to a handful of clubs. When Erling makes the next step, he must be the finished product, perfect. He is very, very good.
“He must improve some details. Robert [Lewandowski] was complete when he left for Bayern [Munich on a free transfer in 2014]. It was clear: He went straight into the starting line-up.
“But as a counter-example, Ousmane Dembele maybe left for Barcelona a moment too early. Erling is far in his development, but he is not complete.”
