UEFA president Aleksander Ceferin has not ruled out fans being able to attend the final stages of this season's Champions League and Europa League competitions.
European football's governing body confirmed on Wednesday that the quarter-finals, semi-finals and finals of both competitions will be staged as mini-tournaments in August.
The Champions League will conclude in Lisbon between August 12-23, with Cologne, Duisburg, Dusseldorf and Gelsenkirchen to host the closing states of the Europa League from August 10-21.
At present, the plan is to hold all of the single-leg ties behind closed doors, although Ceferin told a virtual news conference that the situation remains fluid and an improvement in the coronavirus outlook across the continent could see games played in front of supporters.
"If I would answer today, then we don't think we can have spectators at the Europa League and Champions League quarter-finals, semi-finals and finals," he said.
"But things are changing. Theoretically, a month ago I couldn't even answer if we could play the competition. Now we will play it, hopefully.
"We haven't decided yet about no spectators or spectators because we will assess the situation at the beginning of July and then we will see what the situation will be.
"It would be incompetent for us if we were to decide in advance about a situation that is so unsure at this moment.
"We don't know if only the local fans, if no fans or even the fans from different clubs can travel to the venue.
"The beginning of the Champions League final eight is almost two months from now. Remember what the situation was in Europe two months ago. Things are changing, we have to wait but we will decide, of course, before the draw."
That draw will take place on July 10, by which time the clubs with last-16 ties to conclude in the Champions League and Europa League will know whether those matches are to be played at the originally intended venues or on neutral ground.
"We think there is still a bit of time to understand the situation about travelling, boarders and quarantine, etcetera before we need to know where they will be played," UEFA's deputy secretary general Giorgio Marchetti said.
"In principle, these are return matches – not like the quarters and semis, which have been decided to be played over one leg."
Juventus v Lyon, Manchester City v Real Madrid, Bayern Munich v Chelsea and Barcelona v Napoli are the outstanding Champions League matches in the first knockout round and will take place on August 7 and 8. RB Leipzig, Atalanta, Atletico Madrid and Paris Saint-Germain have already secured their places in Lisbon.
In the Europa League, six second legs will be completed across August 5 and 6, with Inter v Getafe and Sevilla v Roma to be staged as one-off games.
Ceferin added: "For sure, the clubs would prefer to play at home but for now we don't have enough information to decide. For us, health and security is first.
"But when you speak to the clubs, of course clubs would prefer playing at home, even without spectators, rather than on a neutral ground."