The Holland left-back is set to sign for Manchester United in a deal rising to €17m.
Ponsot says they made an attempt, but found the terms demanded too rich for them.
"We will never endanger the club for a player," he said.
"If we do not have the means to buy we cannot take players of this level, regardless of their love of OL or not."
The reference is to some requests made by the player's entourage that led to the deal collapsing.
To remove any doubts, Ponsot added on Friday: "He hasn't signed with anyone yet, but it's over for us."