MLS organisers fear the 2020 season may have to be shortened as a return to action in May is now considered "extremely unlikely".
The league was suspended on March 12 after just two rounds of matches due to the coronavirus pandemic, with May 10 earmarked as a possible date to resume the competition.
However, it is now feared a return to action next month will be impossible and there are concerns it could become difficult to play the full season if the league's suspension continues.
"Although we hoped to return to play in mid-May, that is extremely unlikely based on the guidance of federal and local public health authorities," a statement from MLS on Tuesday said.
"Our goal remains to play as many games as possible, and while we currently have enough dates to play the entire season, we recognise at this time that it may become difficult to do so.
"We continue to learn more every day from the medical experts, and we expect to have additional details in the coming weeks regarding when we can return to play. As we have throughout this process, we will update our fans with every decision, and we thank them for their support and understanding during this extremely challenging time."
The United States has been one of the nations hit hardest by the COVID-19 crisis, with more than half a million confirmed cases and over 24,000 deaths.
As well as matches being put on hold, clubs were instructed to close training facilities until at least April 24 by the Centers for Disease Control and Prevention (CDC), although players requiring treatment or rehabilitation are exempt from the directive.