Chelsea midfielders N'Golo Kante and Ruben Loftus-Cheek will miss the club's pre-season tour of the United States because of their Covid vaccination status.
But travellers who are not fully vaccinated against coronavirus are not allowed to enter the United States.
Currently only US citizens are allowed to enter the country if they are not fully vaccinated.
"N'Golo Kante and Ruben Loftus-Cheek will not travel due to their Covid vaccination status," Chelsea said in a statement.
Chelsea are due to play three pre-season friendlies in the United States.
They face Mexico's Club America in Las Vegas on 17 July, Charlotte FC at their Bank of America Stadium on 21 July and London rivals Arsenal in Florida on 23 July.