“The grass is not always greener" - Mats Hummels fires transfer warning to Erling Haaland amid rumors of a big-money transfer 

Borussia Dortmund's Mats Hummels has given a stark warning to Erling Haaland regarding a potential transfer to Manchester United or Manchester City.

The Norwegian forward has been a force to be reckoned with ever since he made the move to the German side. BVB held onto their key man last summer amid interest from Europe's elite clubs, including Real Madrid, Manchester City and Manchester United.

However, the 32-year-old defender has stated that there's no valid reason for Haaland to leave "The Yellow Wall," as big money moves don't always work out.

Here's what he said:

"I would fully understand him wanting to stay. Because things are really great in Dortmund because he knows what he has here. I have far from given up hope that he will stay for a long time. The grass is not always greener on the other side. You really have to be aware of that in football."

He added:

"It's worth a lot if you have a good environment, feel comfortable with the guys and can also be really successful. You have to value that, that's not a given at every club. So we have a lot to offer to Erling."

Mats Hummels left Dortmund for Bayern Munich in 2016. However, he returned to Signal Iduna Park three years later and is fully aware of the expectations that arise with a move to a bigger club.

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Will Erling Haaland leave Borussia Dortmund next year?

Since arriving at the German club, Haaland has netted 68 goals in 67 appearances, inlcuding 13 goals in the Champions League.

Manchester City have been linked with the Norwegian forward after they failed to sign Harry Kane this summer. According to recent reports, Pep and co. will go all in to bring Haaland to Man City.

On the flip side, the red side of Manchester, too, has been linked with the 21-year-old. However, Manchester United will want to bring a midfielder on board if Paul Pogba refuses to extend his contract.

Borussia Dortmund v 1. FC Union Berlin - Bundesliga

Haaland could also be an option for PSG, more so if Kylian Mbappe finally makes the move to Real Madrid on a free transfer.

Chelsea, too, were also part of the mix. However, they have seemed less interested since Romelu Lukaku's glorious return to Stamford Bridge.

Borussia Dortmund v 1. FC Union Berlin - Bundesliga

With how things are shaping up, Manchester City seem to be in the lead to sign Erling Haaland, and it's safe to say that his father's endorsement will play an instrumental role, who used to play for City as well.