The report claims United chief scout Jim Lawlor flew to Spain to meet the Alcantara camp but a move failed after the club received 'conflicting reports' about the player's transfer cost.
In the end, Thiago moved to Bayern Munich for £21.6m - in the process linking up with former-Barca boss Pep Guardiola.
The 22-year-old Spain international reportedly had a buyout clause in his contract, but confusion over the true figure cost United dearly.
They ultimately decided to pursue other targets, with Lawlor also drafted in on negotiations over a move for Thiago's former-teammate Cesc Fabregas.
But that failed as well, leaving United to chase Ander Herrera and Sami Khedira - although they ultimately had to settle for a deadline day £27.5m capture of Everton midfielder Marouane Fellaini.
And the transfer window struggles at Old Trafford have reportedly prompted David Moyes to overhaul his scouting system.
The new United boss wants to bring in some of his former-Everton staff after conducting a post-mortem on the failures this window.
The club has dismissed calls to appoint a director of football and will instead focus on improving its scouting methods, according to the report.