Maguire signed a new deal with the Foxes last week.
"I was first and foremost delighted he was fit and available," the 57-cap former defender said ahead of Tuesday's friendly against Switzerland in Leicester.
"The reason for that being when I was watching him during last season I knew that on the biggest stage he'd be able to perform and excel.
"I was so pleased he was going to have the opportunity to do that and he delivered.
"He's a superb defender, he's really effective in both penalty boxes and the way that he brings the ball forward and can use the ball is as good as anything in Europe, in my opinion.
"I think he proved to himself as much as anything that against some top players and some top teams in the lead-up to the finals, during the finals and again Saturday night that he can compete with the very best."