Bailly returned to the United lineup in the 2-1 win over Middlesbrough on Saturday, in what the Portuguese later revealed would be his final game before the tournament.
United had hoped that the Ivory Coast international – only recently back from a knee injury – would be available for the trip to West Ham, with the club optimistic of delaying his departure by 24 hours.
However, Les Elephants boss Michael Dussuyer has insisted that the 22-year-old join up with his country at the earliest available opportunity – the FIFA-mandated date of January 2.
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“Bailly is leaving – he goes to the national team,” said Mourinho on Saturday.
“He has to be in the national team on the second of January. We asked them for him to be [here] until the third. They refused, so he cannot play against West Ham.
“I know I lose Bailly for a month so I’m going to have Smalling, Rojo, Jones – three players for eight matches.”
On the subject of the tournament in Gabon, and Bailly’s involvement, Mourinho quipped: “I wish Ivory Coast to be champions. With these kind of decisions, because they are controlling every second, for sure they are going to win the African Cup.”