Dutch champions Ajax admitted Thursday that they had made a "huge" mistake in failing to register record signing Sebastien Haller for the remainder of their Europa League campaign.
The Franco-Ivorian striker joined the club from West Ham in early January for a club record 22.5 million euros ($26.9 million) and ought to have been included on their Europa League roster but somehow was overlooked.
"It's a huge administrative error on our part," Ajax coach Erik ten Hag said on the club's website.
"Something went wrong, an administrative error with major consequences. But as long as there is a chance that we can still register him, we have to go for it. We did not get him for nothing."
Ajax face French club Lille in the round of 32 on February 18 and 25.
Since his transfer, 26-year-old Haller has stood out with two goals and four assists in six Eredivisie appearances.
"It's an incredible setback for him but he's realistic," said Ten Hag.
"He's pretty unperturbed. He was on fire at practice this morning."
Ajax have announced that they will take action with UEFA to rectify Haller's omission.