The Netherlands Under-21 international moved to Stamford Bridge during the summer, but despite opportunities looking limited with the Blues, Overmars has revealed that Van Ginkel was not allowed to leave the club on a temporary basis.
The 40-year-old told De Telegraaf: "He made no mistake, because he really wanted to come to Ajax, but Chelsea did not let him.
"Would it have been better for his development to go to Ajax? Yes, 1000%.
"We tried to get him on loan in this transfer window but unfortunately, Chelsea would not let him go."
Van Ginkel has played just 11 minutes of Chelsea's opening three Premier League fixtures.