Ronaldo is set to miss training for the second successive day on Tuesday due to 'family reasons'.
Erik ten Hag's side fly to Bangkok on Friday for a lucrative 16-day trip which also includes games in Australia.
Ronaldo has asked United to consider offers for him this summer, but the club insist their most famous player is not for sale.
The 37-year-old is said to want to play in the Champions League for the remainder of his career, which the Red Devils won't be doing next season after finishing sixth in the Premier League.
Chelsea have been heavily linked with a move for the Portugal superstar, while Bayern Munich and Napoli have also been linked.
Ronaldo had been expected back at United's training ground on Monday for showdown talks with new boss Ten Hag.
His absence due to 'family reasons' has delayed that and has potentially thrown their summer transfer plans in doubt.
He only returned to Old Trafford last summer from Juventus, in an initial £12.85m deal, and signed a two-year contract.
Ronaldo scored 24 goals in 38 total games for the club in his first season back, but now his future remains uncertain.