The Red Devils booked their place in the FA Cup last four thanks to a 2-0 win over Brighton and Hove Albion in the quarter-final.
Manchester United are looking to win silverware in successive seasons under Mourinho following their EFL Cup and Europa League triumph last term.
The 20-time English champions lost 2-0 to Tottenham Hotspur in the Premier League at Wembley back in February.
Spurs secured their spot in the semi-final draw thanks to a 3-1 win over Swansea City at the Liberty Stadium last weekend.
Tottenham are in fourth place in the Premier League table and four points behind Manchester United in the race to secure a Champions League spot.
Former Arsenal defender Keown believes Spurs are favourites to beat Manchester United in the FA Cup semi-final next month.
“Manchester United v Tottenham could be an epic,” Keown told the Daily Mail. “These two teams need to win a trophy more than anyone else.”
“This could be a defining moment for Mauricio Pochettino — but equally Jose Mourinho has the experience of finding ways to win these matches.
“Often he will copy the opposition’s formation, absorb them and then punish them on the counter-attack.
“Tottenham are the better team and right now I would say they are favourites… but Mourinho knows how to get it right when it matters most.”
Manchester United were 2-1 winners against Crystal Palace in the FA Cup final under Louis van Gaal in May 2016.
Tottenham are looking to win their first trophy under Mauricio Pochettino and their first FA Cup since 1993.
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