"You cannot compare Mikel with Lionel Messi anymore. Messi has gone very far ahead of Mikel because Mourinho changed Mikel's game by converting him from an offensive player to a defensive one," Siasia told the Daily Sun.
"The Mikel I trained for the WYC in Holland was an offensive midfielder. He was very good and outstanding at the Championship. He could pass the ball to strikers, create chances and shoot at goal. These days, you can count how many times Mikel shoots at goal when he is playing in the Premiership.
"That's why Messi is doing better than him today. From the best player at the Junior World Cup, Messi has graduated to become the world's second best player."
Former Nigeria World Cup captain Siasia also said: "(Jose) Mourinho is a different coach. He had other good players in the midfield like Frank Lampard, who can score goals even from a distance. That's why he had to play Mikel as a defensive midfielder. But I still consider him as an offensive player. He can run all day on the pitch. He played his heart out as an offensive player in Holland."