Ireland stunned world champions Germany 1-0 thanks to Shane Long's 70th-minute strike on Thursday to throw Euro 2016 qualifying Group D game.
De Boer, who lasted only 77 days as Crystal Palace manager after losing his first four league games in charge with no goals scored, said in an interview on BT Sport that it was "a pity" Mourinho was Rashford's manager because he was not getting enough chances.
Toni Kroos struck with a fierce long-range shot a minute from time to give Germany a 1-0 victory over Spain in a friendly between two injury-depleted European heavyweights in Vigo on Tuesday.
Images from the 2018 World Cup qualifiers played in Europe on Monday
Spain started their World Cup qualifying campaign with a crushing 8-0 win over Liechtenstein, laying down a marker in Group G with a ruthless second-half display on Monday.
Spain strolled to a 4-1 win at home to Israel, while Italy survived some first-half scares on the way to a 2-0 win and Ukraine registered a 1-0 home win over Ukraine in an action-packed game.