B-SAD was forced to face Benfica on Sunday (AEDT) with just nine players - including two goalkeepers - after positive tests for 13 members of the squad.
Benfica went into half-time 7-0 up and B-SAD was forced to forfeit shortly after the restart due to insufficient players as injuries reduced the host - which was without any substitutes - to six men.
Among the B-SAD players to miss out was Cafu Phete, who had recently spent time in South Africa - where the Omicron variant was first detected - and it now appears that he and the other 12 members of the squad have tested positive for this new strain of coronavirus.
"Preliminary tests carried out at INSA strongly suggest that all 13 cases associated with players of Belenenses SAD are linked to the variant of concern Omicron," INSA's statement to Publico read.
"The predictive value of the tests carried out is already very high."
Benfica's players are set to be tested as Portuguese authorities respond to the Omicron variant being found inside the country's borders.
"We'll have more proactive isolation and a more intensive testing of contacts," Graca Freitas - Portugal's Director-General for Health - told TSF.
Flights into Portugal from Mozambique have now been banned, while two positive cases were discovered among the 218 people to have arrived on the last such flight on Saturday.