The Bayern defender, who was linked with Chelsea, Newcastle and Barcelona, will see his current contract with the German club expire at the end of the season.
Bayern reportedly attempted to renew Sule’s contract by raising his salary to £8.3m (€10m), but the player rejected the lucrative offer from the Bundesliga outfit.
Dortmund announced earlier this month that Sule would leave their arch-rivals in the summer and play at the Westfalenstadion from the 2022-23 season.
Sule, who was signed by Bayern from Hoffenheim in an £18m deal in 2017, has reportedly inked a four-year deal with Dortmund.
Matthaus has claimed that the 26-year-old Bayern centre-back’s move to Dortmund wasn’t motivated by money and he is instead “looking for a sporting challenge.”
The 60-year-old German legend insisted that Sule would have moved to England if money was so important, pointing to the “offer” Newcastle tabled for the player.
Speaking to Sky Germany, Matthaus said: “It is not about money. Otherwise, he would have gone to England.
“He had an offer from Newcastle United, where he would have earned twice as much.
“He is looking for a sporting challenge. And at Bayern, he no longer felt valued. In recent years, Sule has often been attacked because of his weight and no-one has protected him.
“During his long injury break, he sacrificed himself for the club. He won the Champions League and played great games.
“The club didn’t get enough. And I know that is the reason why Sule said to his team of advisors, ‘We don’t need to talk to Bayern anymore. I want to go.’”
Sule has made 162 appearances for Bayern and has lifted four Bundesliga titles, a Champions League, two German Cups and four German Super Cups with the club.
Dortmund sporting director Michael Zorc welcomed the signing of the Germany international from Bayern.
“We’re delighted that we have managed to sign Niklas Sule, a Germany international, on a free transfer and have tied the player down for four years,” he told the club’s website.
Sebastian Kehl, who will succeed Zorc as Dortmund sporting director in the summer, added: “Niklas has shown during the course of personal talks that he is really keen on Borussia Dortmund.
“He possesses a lot of experience, composure in his build-up play and the necessary physicality to take the next step with us from this summer onwards.”
Newcastle reinforced significantly in the January transfer window with the arrivals of Bruno Guimaraes, Chris Wood, Kieran Trippier and Dan Burn at St James’ Park.
Featured Image Credit: PA
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