The Holland international struck 29 goals in 32 Bundesliga games as the German side finished third and has once again drawn interest from a host of leading Premier League sides.
Manchester United have held a long-standing interest in Huntelaar whilst North London rivals Arsenal and Tottenham are looking to add a prolific frontman to their squad ahead of next season.
And Heldt has confessed that the 28-year-old can leave the Veltins-Arena after disclosing that a bid €20 million (£17m) will trigger the release clause allowing clubs to talk to him about a transfer.
“Huntelaar does have a €20 million buyout clause, and the rich club can afford it,” Heldt told Bild.
“But, Klaas Jan has always stressed that he wants to be a champion. This he can be only with Real or Barcelona in Spain.
“I do not think he wants to go there. What would he do there? Since nothing more than the weather is better.”
With Dimitar Berbatov set to leave Old Trafford a striker has jumped to the top of Sir Alex Ferguson’s shopping list and Huntelaar could be the man to fill the void although he can expect competition from Arsenal and Spurs.
The former Ajax star endured a difficult spells in Spain and Italy prior to his move to Schalke where he has re-discovered his goalscoring prowess.
He signed for Real Madrid in January 2009 but failed to adapt in La Liga scoring just eight in 20 appearances while at the Bernabeu and was sold just six months later to AC Milan but failed to nail down a regular starting spot at the San Siro and left a year later.