According to the Manchester Evening News, the Red Devils shot-stopper has not been training at United’s Carrington complex for the past week.
The Argentine is instead believed to be training back in Buenos Aires, and is expected to move to Boca Juniors ahead of this summer’s Copa America.
United gave Romero the green light to leave the UK to train in Argentina.
But should his switch fall through this month, the goalkeeper will be expected to return to England and train with the Manchester United squad.
Romero’s Red Devils contract expires at the end of the season.
United have the option to extend it for another season, but Ole Gunnar Solskjaer left the keeper out of his Premier League and Champions League squads this campaign.
This means that if Romero doesn’t complete a move to Boca this month he will likely be allowed to leave United on a free at the end of the season.
Romero fell down the pecking order at United due to Dean Henderson’s assured performances between the sticks while on loan at Sheffield United.
Henderson is behind David de Gea in the pecking order but kept goal for United in Wednesday night’s clash with Manchester City.
The keeper was beaten twice in the Carabao Cup semi-final as Pep Guardiola’s Man City ran out 2-0 winners at Old Trafford.