The right-back made his first start for England in Tuesday night's friendly with Sweden at Wembley, and was named man of the match for his performance in his side's 1-0 victory.
And Defoe has praised the youngsters achievements.
“It’s not easy, getting man of the match for England, let alone on your full debut - there are so many other quality players out there," Defoe told Tottenham's official website.
“It’s special for him. He’s only 20 and to get into the full England squad and to be voted best player on the pitch, that’s unbelievable really.
“It doesn’t surprise me though. He was fantastic on loan at QPR and Villa last season and he’s done really well for us this season.
Walker's form at club level has been equally impressive, with the former Sheffield United defender cementing a place in Harry Redknapp's first choice back four, and even scoring a late winner in last month's North London derby at White Hart Lane.
And Defoe has named Walker's pace and power as among the attributes that have seen the Sheffield-born youngster made such a big splash this term.
“He’s such an athlete. He’s strong, quick, aggressive, he can defend and is so good going forward.
“I think he could be the England right-back for years to come. He’s got everything to be a top player and to go on and play in plenty of tournaments for England."
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