United reached an agreement with Real Madrid for Varane on July 27.
The 28-year-old French defender is based in Manchester. But missed Friday’s league deadline to register him over the weekend due to quarantine rules.
“Things happen and things take time, it will be done soon,” said United manager Ole Gunnar Solskjaer.
“Unfortunately, loneliness delays these things.”
The UK government’s coronavirus travel rules require people arriving from certain countries to spend a certain amount of time apart.
Solskjaer says the transfer is still complete.
Raphael Varane said: “Not 100% done yet. He hasn’t trained with us yet and we haven’t put all the dots on the i and cross the t.”
Edinson Cavani, Eric Bailly and Amad Diallo were also unavailable for Saturday’s match.
“Adie is in the country,” Solskjaer said. “He just ended his quarantine period. He had a little extra time for personal reasons.
“Eric and Amad are also in the country awaiting clarity to join the team again.
“Of course they had a very exciting summer. also went to the Olympics and played games before that as well. So they should be fit before they arrive.”