There is no valid answer because in almost all Manchester United matches, Erik ten Hag always plays Onana as the main choice.
Without Onana, Cameroon won against Gambia and Cameroon qualified for the next round with Senegal who were group winners.
Ondoa played well based on the statistics he obtained and this is far from Onana's statistics when Cameroon lost to Senegal.
ten Hag will watch and assess Manchester United's second goalkeeper during the FA Cup match. If it is still possible, ten Hag will look at and assess the second goalkeeper again when Manchester United plays Wolves. The second goalkeeper's statistics will be comparable to Onana by him.
To be objective, Onana is not such a reliable goalkeeper for Manchester United that his absence could be decisive, especially in cup matches. Ten Hag should think about the Premier League, does he have a chance to get into the top 4. Now they are 11 points behind Aston Villa, and given how strong the leaders are now, I don’t believe that Manchester United have any chance of joining the title race. Manchester United even has a negative goal difference, which says a lot.