Representatives of Mourinho spent Tuesday negotiating personal terms with the club's executive vice-chairman Ed Woodward and talks are understood to have been positive.
It is expected that he will be confirmed as Van Gaal's replacement at some point this week.
As revealed by The Independent yesterday, Mourinho has already identified both Karim Benzema, the Real Madrid striker, and Zlatan Ibrahimovic, whose contract at Paris Saint-Germain is about to expire, as key transfer targets.
Karim Benzema to Manchester United: Jose Mourinho identifies Real Madrid striker as priority transfer target
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What will be in Jose Mourinho's in-tray?
Memphis Depay says working with new manager would be 'nice prospect'
Which players may find themselves on the Old Trafford transfer list?
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