The striker left Mainz in January for a move to England. Palace signed centre-forward Mateta on an 18-month loan arranagement from Bundesliga outfit Mainz.
The deal for the Frenchman, 23, who had scored 10 goals - including seven in the Bundesliga - prior to the move, came with an option to buy.
For Heidel, there's no regrets over Mateta's departure, insisting Mainz are now in a better place after his exit. Indeed, while Heidel was a fan of Mateta, he insists the centre-forward's style of play didn't suit the system Mainz now employs.
"With Mateta and his seven goals we got six points in the preliminary round and now twelve without him," argued Heidel to BILD via Fussball Transfers.
"He is without a doubt a good striker, but he does not fit our style of play and also wanted to leave the club.
"That's why this question doesn't arise for us."
Despite Heidel's claims, Mainz now sit inside the Bundesliga dropzone in 17th place, three points from safety. Mateta, meanwhile, has played four times for Crystal Palace since his arrival, scoring once.
Overall with Mainz, Mateta played 71 times, scoring 27 goals across all competitions.
- updated March 10
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