The 18-year-old attacker has signed a long-term contract until June 2031, with reports suggesting the deal could be worth up to £8 million.
After growing up in Australia, he joined Manchester City’s academy at the age of eight and quickly progressed through the ranks.
He made his senior debut in the Carabao Cup last season and also scored the winning goal as City lifted the FA Youth Cup.
Heskey has represented England at youth level, scoring seven goals in 22 appearances across the Under-17, Under-18 and Under-19 teams.
“Reigan has developed incredibly well in the past few years with Manchester City and is one of the most exciting attacking talents in his age group,” said the club’s Managing Director, Thomas Kessler.
“His development is not over by a long stretch. We see a lot of potential in him, and we are convinced that he can make the step up to the next level at FC.
“In René, we also have exactly the right coach to guide him along this path, thanks to his motivational approach and his excellent rapport with young players.
“Reigan has a lot of qualities: he’s physically strong with a real eye for goal. He has a lot of pace, and is able to play in several positions.”