England face Germany in their last game of Euro 2020, with former Chelsea, Manchester United and Spurs boss Mourinho believing the winner will head to the final.
Southgate cut and changed their squad throughout the group stages, but their judgments paid off as they outscored Group D without conceding a goal.
Grealish was left out of the starting XI against Croatia and Scotland but was in great shape in the win over Czech Republic as he assisted in Raheem Sterling’s opener.
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And Mourinho believes the Aston Villa star, who has been linked with a move to Manchester City, deserves to keep his place alongside Mason Mount, who has just come out of isolation, missing.
He also wants his former United player Luke Shaw to be given the green light after the full-back hit the head coach this week after Mourinho continued to criticize him.
The Portuguese manager also believes England should settle down with three full-backs from Kyle Walker, John Stones and Harry Maguire, with Shaw and Reece James as full-backs.
Declan Rice and Kalvin Phillips were approached to protect the defense by holding midfielders with Grealish backing Sterling and Harry Kane in attack.
The Roma boss also believes that if the Three Lions can navigate a tough game against the Germans, they will reach the final with Denmark, Czech Republic, Ukraine and Sweden on their side.
He told TALKsport: “Sweden, Ukraine, Denmark, Czech Republic… Come on, beat Germany and they will go to the final. “
Southgate played down revenge talks after England were beaten by the Germans in penalties in the Euro 96 semi-final.
But Mourinho is not buying it and believes there is definitely something more after his infamous missed penalty.
He said: “I don’t think Gareth forgot it.
“I never forgot a few important shots on goal that I lost and I was not a taker. He never forgot it. There is only one way for him to forget it and that is tonight.
“His team to beat Germany and go, so I think, to the final.
“When you look at what we can get after this, of course good teams, Sweden, Ukraine, Denmark, Czech Republic, but tonight is the semi-final for me. ”
Mourinho predicted England XI against Germany : Pickford; Walker, Stones, Maguire, Shaw, James ; Phillips, Riz; Grealish, Sterling, Kane.