It doesn't look like Athletic Bilbao has complained about the situation.
The source is Fabrizio Romano again so this very awkward...
He is still keen on completing the deal. Barcelona is only needed to pay for Nico's release clause and that's it. They just don't want any installments like I said before.
I hope Barcelona finishes it without making a regulation breach.
It was reported some days ago that Athletic Bilbao called on the La Liga organizers to look into Barcelona’s financial situation to see if they are able and fit to make such a transfer because they don’t want to lose their key player. However they can still hold Barcelona down if they ask that his release clause be paid in full at one go instead of in installments, this could be a problem for Barcelona and could help them secure their player.