The arsenal site lists it as actual players as well as staff that met the Olympiacos owner.
Some players are self isolating, as well as some staff.
The below is took from the Arsenal link -
Following yesterday’s news that Olympiacos owner Evangelos Marinakis has recently contracted Covid-19, we have been taking medical advice and tracing any individuals who had what the guidelines define as close contact with him at the game 13 days ago.
As a result of this exercise we identified that a number of players met the Olympiacos owner immediately following the game.
The medical advice we have received puts the risk of them developing Covid-19 at extremely low. However, we are strictly following the Government guidelines which recommend that anyone coming into close contact with someone with the virus should self-isolate at home for 14 days from the last time they had contact.
As a result, the players are unavailable for tonight's match against Manchester City and the Premier League has decided the game should be postponed.
The players will remain at their homes until the 14-day period expires. Four Arsenal staff, who were sitting close to Mr Marinakis during the match will also remain at home until the 14 days are complete.