The Gelsenkirchen outfit are keen to strengthen their squad after an underwhelming 2016-17 campaign in which they had to settle for 10th place.
Adding some fresh blood to their midfield is seemingly one of Schalke's main priorities and Harit is one of the names on their shortlist.
"Harit is a very interesting player," Heidel told Kicker. "He is one of a number of options.
"We will have to look at how realistic a transfer is from a financial perspective."
The 19-year-old came through the ranks of the Nantes youth academy and has developed into an important first-team member since making his debut in August 2016.
Harit has a contract with Nantes until June 2020 and could reportedly cost up to €15million.
He is reported to have been scouted by Premier League heavyweights Arsenal towards the end of the 2016-17 campaign, but could now be heading to the Bundesliga.