One of Chelsea's high-profile acquisitions in January will have to be left out of the team for the Champions League.
In the round of 16, the Blues will face Borussia Dortmund, with the first leg taking place in Germany on February 15 and the second leg taking place at home on March 7.
With Enzo Fernandez becoming their eighth addition in a British record £107 million move on deadline day, owner Todd Boehly finished his spending binge this month.
Other additions include the loaned Joao Felix from Atletico Madrid, the £88 million Mykhailo Mudryk, and the £35 million Benoit Badiashile.
Only three new players may, however, be registered for the knockout stages according to UEFA regulations.
Chelsea must choose by Thursday night which three of the eight newcomers Graham Potter will join to their roster.