Evans has signed a short-term deal at Old Trafford to allow him to feature in the club's preseason matches. He made his first United appearance for eight years in the 1-0 win over Lyon in Edinburgh on Wednesday.
The 35-year-old has not been picked to travel to New York with Erik ten Hag's senior squad but will instead join a group of young players for the game against Wrexham in San Diego.
Sources have told ESPN that Ten Hag has been impressed with Evans after joining training sessions at Carrington and remains open-minded about whether there is a place for the centre-back in his squad for next season.
There remain doubts about Harry Maguire's future after he was stripped of the captaincy last week. There is interest in the England international from West Ham and Tottenham and should Maguire leave, Evans would be a ready-made replacement in a summer during which transfer funds are tight.
The final paperwork is due to be signed on Thursday and Onana is already on his way to link up with the squad in New York. The 27-year-old, who is arriving in a €55 million ($61.2m) deal, could make his first appearance for United against Arsenal at MetLife Stadium in New Jersey on Saturday.