Premier League clubs will have to consider quarantining players for up to 14 days in hotels before matches resume.
The warning came as the 20 clubs voted unanimously for the stage one of the return to training protocols as part of Project Restart.
It means that once the results from the testing of players come through today the first training sessions can start around 2.0pm.
The agreement is the first step towards a return to football, with steps two and three to follow, but Dr Mark Gillett, the Premier League's medical adviser and the architect of the return to group training protocols, said the final stage could include isolating players as has happened in the Bundesliga.
In Germany, the players spent seven days before the games resumed in hotels but Dr Gillett said the advice from Public Health England was that isolation was only effective for a two-week period and that this may have to be followed.
"The advice we have from Government is that if you are going to isolate you have to do it for 14 days," Dr Gillett said. "So you need to be in a hotel environment for 14 days to make it truly effective.
"Now that's certainly something we are going to need to think about and consult widely with players, clubs, managers, PFA, all the stakeholders as we move through to that phase. It is certainly something that will be discussed and ultimately when we get to phase three in particular we will make a decision on that and it will be one that everybody is happy with."
Richard Masters, the Premier League's chief executive, said that June 12 remained a "staging post" for the restart of matches, although there is a widespread acceptance that it is likely to slip by at least a week.
"Next week we are going to be discussing full contact training protocols," Masters said. "Once we know we can start that and had a proper discussion with the clubs as to how much is required we will then be in a position to confirm when the season start date is. We have to be flexible about it and don't want to continually move that. We are in a step by step process."
Masters said he hoped that the concerns of players and managers had been allayed by the strict protocols put in place for the return to group training - including social distancing and hygiene measures.
"Clearly we cannot de-risk the entire thing but what we have created is an extremely safe environment for this first stage. Hopefully we have reassured all players and managers," Masters said.
The Premier League is likely to be given extra time to decide when it hopes to restart the 2019-20 season, after Uefa yesterday moved its executive committee meeting back from May 27 to June 17.
Players and managers, including Manchester City's Raheem Sterling, have insisted adequate time must be factored in between the resumption of regular contact training and any season start date.
The first step requires training to last for no more than 75 minutes for any single player, and with groups of a maximum of five players in each mini-session.
Players will be asked to leave three parking spaces between their vehicle and any other at the training ground, and arrive wearing kit. There will be no access to communal areas such as canteens.
All equipment will be disinfected by club staff wearing personal protective equipment (PPE) and players must wear face coverings at all times.
An app will be used for players to provide daily updates on their condition.
There have been concerns raised by Premier League medics over their liability should any staff fall seriously ill.
The league's director of football Richard Garlick said: "We have spoken to the insurers both in relation to the liability insurance for the clubs but also indemnity insurance for the doctors. It's in our protocols.
"They are content with them."