Portugal detected 13 cases of the Omicron variant of the coronavirus on Monday, all involving players and staff members of Lisbon football club Belenenses SAD, after one player recently returned from South Africa, health authority DGS said.

The new variant, which according to the World Health Organization is likely to “spread internationally”, was found after Belenenses played a Primeira Liga match against Benfica on Saturday.

The game started with only nine Belenenses players on the pitch because the rest were isolating and only seven returned to the field after half-time. The match was abandoned two minutes into the second half with Benfica leading 7-0.

A club spokesman said 44 players and staff, including himself, were self-isolating at home and waiting to repeat the tests.