The 22-year-old is believed to have agreed terms on a five-year deal worth £100,000-a-week at Old Trafford with United now hoping to push through a deal over the weekend with further talks with Barca planned.
Should United, as expected, finalise a deal, Thiago would become new boss David Moyes' first major signing since taking charge in what would be a signficant coup for the club.
Barca are loath to lose their young midfield maestro, who underlined his quality by scoring a first-half hat-trick in Spain's 4-1 win over Italy in the European Under-21 Championship Final earlier this week.
- VIDEO: Thiago treble fires Spain U21s to Euro glory
However, they are effectively powerless to prevent him leaving the Camp Nou should clubs meet his £17m release clause which was activated after he failed to make enough first-team appearances last season. The option, however, is only valid until August 1.
A message, presumably written by team-mate and United star David De Gea on Thiago's match ball after his Euro Under-21 final showing, read 'see you in Manchester' in Spanish, hinting that a Old Trafford deal was close.
Reports clain the player's father and former Brazil international, Mazinho, has held talks with United officials to iron out personal terms and is happy that the Premier League champions are the right club for his son to continue his footballing education.