Uefa has warned that the staging of international matches will be at risk if its protocols for the return of the Champions League and Europa League are not observed.
Both tournaments resume this week after a five-month delay because of the coronavirus pandemic.
The protocols were distributed to all 28 teams still in the two competitions.
Both competitions conclude with 'final eight' tournaments behind closed doors in Portugal and Germany.
The Champions League final will be held in Lisbon on 23 August, two days after the Europa League final takes place in Cologne.
"Uefa expects all parties to adhere to hygiene best practices both in the controlled match environments, as well as in their private day-to-day lives," the protocols state.
"It is imperative that all precautions set out in this document, as well as the standard hygiene best practices, will be strictly adhered to by all members of these various groups.
"Non-respect of such social norms could have serious consequences for the staging of international matches."
The return of European club competition will immediately be followed by the start of the Nations League international qualifiers at the beginning of September.
In addition, the 2020-21 European club season starts on 8 August, with Northern Irish side Linfield involved in the Champions League preliminary round.
Testing, masks, hotels and private flights
The protocols themselves have been drafted under the guidance of Uefa medical committee chairman Tim Meyer, who is also in charge of the Bundesliga protocols in Germany.
Club players and staff have been told they will be tested either two or three days before they leave their home countries for the 'final eight' tournaments and again, on site, the day before each game.
Uefa promises to have the results back "a minimum of six hours" before kick-off.
Clubs have been told their players must wear face masks 'in all public places' when they are travelling and the use of charter flights "is strongly recommended".
Players have also been reminded to refrain from swapping their shirts.
Uefa has rejected requests from some clubs - including Manchester United, Wolves and Inter Milan - to be allowed to fly in and out of Germany for individual games, which means more emphasis on the strict rules around the hotels individual clubs are staying in.
Amongst the requirements for that are:
Private dining area and access routes.
Food should be served by the team's own staff and/or as few hotel staff as possible, with food placed on a table and collected by the players/coaches/trainers. No clean-up is to take place until the players have left the dining areas.
Team members (both players and technical staff) must not leave the hotel unless it is under previously agreed and organized conditions and does not involve coming into contact with anyone outside of their group.
For longer stays, visiting teams will also need to make appropriate laundry arrangements with their hotel, ensuring in particular that washed clothing and equipment (bibs etc) are only handled by members of the team delegation and not by hotel staff.