Lionel Messi `unstoppable` in this form: Pep Guardiola

Barcelona: Bayern Munich coach Pep Guardiola believes Lionel Messi is unstoppable on current form as he prepares to face his old club Barcelona for the first time in their Champions League semi-final, first-leg on Wednesday.

Messi and Guardiola won 14 trophies together during the latter`s glorious four-year spell in charge between 2008 and 2012, but insists even he doesn`t have the formula to stop the four-time World Player of the Year, who has scored 51 goals in 50 games this season.

"There is no defence that can stop Messi. It is impossible," Guardiola said on his return to the Camp Nou wearing the colours of the opposition for the first time.

"How he is playing at the moment, you cannot stop him.

"Defending with nine in your area or 11 pressing high. You can`t always be at your best physically during your career, there are ups and downs, but the way he has played the last four or five months there is no way to stop him. He is too good.

"Obviously you have to get close and try to ensure he receives the ball less, but there is not a system or coach to stop talent of his magnitude."