Van Ginkel signed from Chelsea from Vitesse – a club they have a partnership with – for a reported fee of £8million in July.
The 20-year-old Netherlands international is tipped for a bright future, but according to Overmars, was keen on joining Ajax on loan this season to further his development.
Chelsea rejected his request, though, insisting he had a first-team role at Stamford Bridge, and he has featured twice off the bench in the Premier League this season.
Overmars thinks Van Ginkel would have been better served by spending a season at the Eredivisie champions, though.
"He made no mistake, because he really wanted to come to Ajax, but Chelsea did not let him," Overmars told De Telegraaf.
"Would it have been better for his development to go to Ajax? Yes, 1000 per cent.
"We tried to get him on loan in this transfer window but unfortunately Chelsea would not let him go."
