Leicester are chasing the Manchester United legend.
New York Red Bulls coach Backe, who was Sven Goran Eriksson's No.2 at Manchester City, said: "If it is his intention to return to the Premier League, I would say, 'Go for it'. The key for someone his age is physical condition - looking after your body and diet - which has been important to him as he is so fit.
"If anyone is going to do it at that age, it will be David, as he is a top professional.
"The way he has come back after his Achilles surgery last year has been just phenomenal.
"When I was with Sven, he always said David was one of the best, with a character, attitude, spirit and passion for the game which was second to none.
"It was a real privilege for me to work with him for four days."