Following the coronavirus outbreak that infected nearly half of the Miami Marlins' roster and prompted the temporary suspension of the team's season, Major League Baseball is encouraging players not to leave hotels in road cities except for games, mandating the use of surgical masks instead of cloth masks during travel and requiring every team to travel with a compliance officer who ensures players and staff properly follow the league's protocol, sources told ESPN.

The updated rules, outlined in a memo distributed to teams Tuesday, came as MLB investigates the cause of the Marlins' outbreak that has seen 16 players and two staff members test positive for COVID-19, according to sources. The Marlins' games through Sunday have been postponed, and the prospect of their season restarting Tuesday at home against Philadelphia remains in question.

Commissioner Rob Manfred defended the league's protocol in an interview with MLB Network on Monday and could further strengthen it in the coming weeks as the consequences of the Marlins' outbreak become clearer -- particularly regarding the scrupulousness of contact tracing. The league on Wednesday also postponed Friday's scheduled game between the Toronto Blue Jays and Philadelphia Phillies, the latter of whom played the Marlins on Sunday before the scope of the outbreak was clear. The game is set for Saturday, giving Philadelphia an extra day to assess whether the virus was transmitted by the Marlins to any of its players, sources told ESPN.