The event in Muscat on 4-7 March was due to be the first leg of a second Middle East Swing, but it has been reduced to just the Commercial Bank Qatar Masters on 11-14 March.
The tour said the decision had been made "following an announcement by the Omani government that all gatherings, international functions and sporting events are to be stopped in the country with immediate effect".
The organisers are looking into the possibility of rescheduling the tournament, but "there are no definitive plans at this stage".
Last year, the Oman Open, which has been held twice as a main tour event, was the penultimate tournament before the European circuit went into lockdown due to Covid-19.
A number of tournaments were subsequently cancelled, including the 149th Open Championship at Royal St George’s, where the event is now due to take place in July.
Since coming out of lockdown in July, tournaments have been taking place in bio-secure bubbles, with US PGA champion Collin Morikawa among those to praise the safe environments in place on this side of the Atlantic.
"I think the European Tour has done an amazing job with this bubble,” he said ahead of this week’s Omega Dubai Desert Classic. “It's very different than what we have in the US, but they are doing it right.”
However, restrictions have started to tighten up since the 2021 schedule was announced in December, with direct flights from the UAE to Scotland now having been stopped.
Meanwhile, Scotland’s Russell Knox has been nominated to run for chairman of the Player Advisory Council (PAC) on the PGA Tour.
The Florida-based player, who already sits on the group, is up against major winners Rory McIlroy and Kevin Streelman in a vote by fellow players which ends on 11 February.
The winner will take up the role in 2022 for a three-year term, with Knox or McIlroy in line to make history as there has never been a non-American policy board player director.