The midfielder has been linked with a return to his first club Vitesse, with the director of football insisting that the decision to sell lies with the coach alone
The 31-year-old midfielder joined the Amsterdam giants in 2011 on a two-year deal from FC Twente, but has been linked with a move back to the side where he spent the first 10 years of his professional playing career.
Overmars has said that whilst Vitesse have not made any bids, Janssen could still be expected to depart Ajax.
"Vitesse have been linked with Theo, but there is no bid. Frank de Boer and the others in the technical team will decide what they want to do," the former Arsenal man told De Telegraaf.
"If the coach says he cannot leave, then he stays. And I can imagine that he says that, because Theo was and is an important player for Ajax. If Frank thinks he can get a certain amount for him, we will talk then. But for now, there is nothing."
Janssen made 38 appearances for the Eredivisie champions last season, and has one year left to run on his contract.