Chelsea and Spurs have both been hit by Covid cases with the Premier League set for a fresh wave heading into the Christmas period.
Blues boss Thomas Tuchel revealed on Tuesday that Mateo Kovacic had tested positive - a day after returning to training. And Spurs are understood to have had six players and two staff hit by a positive test.
Chelsea boss Tuchel, who takes his Chelsea side to Zenit St. Petersburg on Wednesday said: “I was aware that this can happen. Me personally, I am not happy that it is happening as a manager and person.
“But this is the reality at the moment and we have to be ready to adapt to secure people's health. We have to do the best thing possible to avoid transmission."
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Croatian midfielder Kovacic had missed the Blues' last eight games due to an injury picked up in training in October.
'Mateo was in training yesterday with a big smile and was pure pleasure to have him back,' Tuchel added. “But he tested positive today for Covid and is isolating.”
Spurs are due to face Rennes in a crucial Europa Conference League group game in London on Thursday.
But boss Antonio Conte is expected to confirm on Wednesday that his preparations for all of the club’s pre-Christmas fixtures have been disrupted.
More PCR testing is due to take place at the club’s Enfield HQ over the next 24 hours. But Spurs’ Rennes clash is followed by a Premier League trip to Brighton on Sunday.
Under Uefa regulations, if they have 13 available players, including a goalkeeper, from their 25-man A list, they must fulfil the Rennes fixture, which they need to win to stand a chance of qualifying for the final 32.
The game could be postponed if they do not have sufficient player numbers but all group matches must be completed by 31 December.
It is yet to be established whether the club will contact the Premier League about Sunday's game at the Amex Stadium, but a decision to postpone league matches can only be made by the competition board.
