Malen scored for PSV Eindhoven in their Champions League qualifying win at BATE Borisov.
De Boer recalled: "He has a lot of talent. I know him from his Ajax period. He actually was to be the successor to (Kasper) Dolberg. He then went to Arsenal and did not come back. He is really a good player, but is still a young talent.
"We saw him as a full-fledged Ajax player."