De Boer lasted only five matches at Crystal Palace before being sacked in September.
Rashford, who burst onto the scene unexpectedly during the Louis van Gaal regime, and the subject of De Boer's outburst against three-time Premier League and two-time Champions League victor Mourinho, made 53 appearances in Mourinho's first season in charge, scoring 11 goals, and has made 40 appearances so far this season, bettering his goal tally by one from previous year.
Rashford is Manchester-born, supports United and Reds fans see him as one of their own, another continuation of the club's proud tradition of giving young players a chance.
"If Marcus would be coached by Frank, he would learn how to lose", Mourinho added.
The 20-year-old forward started his first ever Champions League knockout stage match but it ended in crushing disappointment as United crashed out at the hands of Vincenzo Montella's men.
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ET, giving you plenty of time to ignore more of your work before you check out for the NCAA tournament around lunchtime. But the 30-year-old Queenslander attributed it to poor iron play, averaging 51 feet from the hole on approach shots.
Paul Pogba remains a doubt with a leg injury picked up in training last week. "In training is where I'm doing most of my learning".
Not trusting young players is a stick Mourinho has been beaten with since his first spell at Chelsea but a stat has been unearthed that will change your mind on everything you've heard about Rashford recently.
While he might not have meant any offence to the Manchester United manager and might have even praised him indirectly for his winning mentality, Mourinho certainly took it the wrong way.
Neither of those victorious sides were favourites for the crown and the Portuguese believes United are outsiders this time. "But when a team reaches the last eight, anything is possible".
Guardiola, famed for developing world-class players like Sergio Busquets, Gerard Pique, and one Argentine genius by the name of Messi, has promoted. I know that it is very hard to go through. "There comes a time, whether you like it or you don't like it, that your body tells you it is time to stop playing football".