The 25-year-old has won the Ballon d'Or for the past three years and is once again one of the main candidates to win the prestigious individual award this year.
"Right now, there is no-one who can compare with Messi," Rexach told La Xarxa.
"If you look at his numbers, nobody has scored more goals than him. He is setting some unusual records.
"He has won many titles. Finally, looking at what he has achieved, he will be the best. Messi has that gift of appearing and scoring a goal or giving an assist."
Messi has scored eight goals in La Liga and two in the Champions League for Barcelona so far this season.