Haaland is set to become the subject of a bidding war among Europe’s biggest clubs when a £68m release clause inserted into his contract becomes active next summer.
The 21-year-old Norway international has cemented his place as one of the best strikers in world football since joining Dortmund from Red Bull Salzburg in January 2020.
Haaland has scored a remarkable 68 goals in 67 games across all competitions since moving to the Signal Iduna Park and was the Champions League’s top scorer last season.
Despite his impressive strike rate, Hummels has cautioned Haaland that maintaining his current standards may not be a given should he depart for another club.
Speaking to Bild, Hummels said: "I can fully understand him if he wants to stay!
"Because it’s great in Dortmund, because he knows what he’s got here. I haven’t given up hope that he’ll stay for a long time.
“The grass on the other hand is not always greener. You really should be aware of that in football.
“It’s worth a lot if you have a good environment, and you feel comfortable with the boys, too.
“You have to appreciate that. That is not the case in every club. So we have a lot to offer Erling, it is not like that.”
Hummels left Dortmund for Bayern Munich in 2016 but returned after three seasons in Bavaria.