The Spain international is also expected to undergo his medical this evening.
Mata flew to Manchester by helicopter earlier today to meet with David Moyes and have a tour of the club's new training base.
He said his goodbyes to his Chelsea teammates yesterday afternoon and will, all going to plan, train with his new Manchester United colleagues at Carrington tomorrow morning.
Reports suggest that Mata will pen a four-and-a-half year contract worth in the region of £150,000 a week - a considerable increase from his current deal at Stamford Bridge.
He is then expected to make his Manchester United debut against Ole Gunnar Solskjaer's Cardiff City on Tuesday night.
Chelsea, meanwhile, will give the green light to the deal after confirming the £11m transfer of Basel forward Mohamed Salah, who has completed a medical and agreed personal terms with the west London outfit.