Goretzka's contract is due to expire at the end of the season, leading to interest from across Europe, but it has now emerged that the player has passed a medical and agreed a deal to sign for Bayern Munich in the summer.
Heidel said: "Leon Goretzka informed us earlier this week that he wishes to leave the club and join Bayern".
"We were very sorry to hear this. [Bayern chief executive] Karl-Heinz Rummenigge told us yesterday that Leon has completed a medical. We are losing a very, very good player."
The 22-year-old joined Schalke from Bochum in 2013 making 130 appearances and scoring 19 goals.
Goretzka will sign a four-year contract with the Bundesliga leaders, starting from July 1.
19 January 2018