Barkley has long been tipped as a future England regular and has racked up nine senior caps since making his debut against Moldova in September last year.
The 20-year-old has become a key figure in Everton's side under Martinez and his strong performances at Goodison Park last term helped earn Barkley a spot in England's World Cup campaign, where he made appearances in all three games as Roy Hodgson's men crashed out at the group stage.
And having recently urged his star youngster to embrace comparisons with England legend Paul Gascoigne, Martinez believes Barkley has all the tools to become his country's greatest ever performer.
Martinez said: "There is no doubt in my mind he will be the best player England has ever had.
"Ross has everything. Normally a player has the pace and power to get around the pitch, or they have the vision to pick a pass.
"Ross can do both of those things. He is two-footed, he's intelligent and he is also in love with the game.
"All he wants to do is play football. When we played in our first UEFA Cup game this season he was gutted to be injured, because he was desperate to play."
