In the previous transfer window, he has an opportunity moving to Man United but he refused it since Barcelona still didn't pay all his salaries. As far as I know, the reason was about the salary, not about Man United not playing in UCL. Sure, he finally will play in Europa League also because Barcelona seems hard to qualify for the next stage in UCL.

Frank De Jong is no longer a key player for Barcelona, he spends much time on the bench now. No doubt that he will leave Barcelona if there is a top club makes an interesting offer. Barcelona also needs fresh money to balance the players' salaries. So, it will be good both for De Jong and for Barcelona as well.