The former West Ham man completes a two-year loan deal at Old Trafford this summer, with Sir Alex Ferguson's side having the option to sign the Argentine for a fee believed to be in the region of £20 million.
However, any deal for the powerful front-man has yet to be agreed.
Tevez himself has revealed he expects to leave the Premier League champions this summer, with Liverpool, Manchester City and Real Madrid just some of the clubs being linked with his signature.
While United argue that they intend to negotiate an agreement to keep him at Old Trafford with the player's representitive, Kia Joorabchian.
But Messi, who could line-up against his fellow countryman in next Wednesday's Champions League final in Rome, is perplexed at why the reigning English, European and World Champions are risking losing his services by taking so long to sort out his future.
“I have no idea why Manchester are letting my countryman go," he said.
"He is talented enough to be in every team in the world’s starting line-up."
NEWS: David Gill: United want Tevez to stay
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