It had been thought the Barcelona midfielder had opted to join United after deciding his hopes of securing a place in Spain's World Cup squad were best served away from the Nou Camp.
However, it is now being reported in Spain that Thiago has instead decided to link up with former boss Pep Guardiola at Bayern Munich.
If confirmed the news will be a blow to new manager David Moyes, who had hoped to use Thaigo to bolster a midfield lacking the retired Paul Scholes and for whom the futures of Darren Fletcher and Anderson in particular are uncertain.
Not that these concerns could dampen the enthusiasm of those who turned out to greet United, both at the airport and team hotel this morning.
It is the scale and intensity of support for the club in this part of the world upon which so much of their huge commercial success is based and it would be no surprise to learn the opening game of United's five-match tour of the Far East and Australia, against Singha All Stars on Saturday, is a sell-out.
Moyes' first task, along with Ryan Giggs who has taken on a player-coach role this season, was to sign a book of good wishes for the Thai king, who is so revered in the country.
Although United's players were allowed some rest after their 12-hour flight, a closed-doors training session was planned for later in the day.
With Robin van Persie missing this leg of the tour, which moves on to Australia on Sunday before stops in Yokohama, Osaka and finally Hong Kong on July 29, Wayne Rooney will be the centre of attention.
Rooney's future remains open to doubt despite Moyes' latest insistence the England man will not be sold having returned to pre-season training in good shape - which, by his own admission, has not always been the case.
"The team here are telling me it is the best shape they have seen him in for five years," Moyes told talkSPORT. "I am taking that as a positive.
"The club have already stated Wayne is staying and is not for sale.
"I am going to get the best Wayne Rooney I possibly can."