Bayern Munich head coach Pep Guardiola has admitted that Lionel Messi is unstoppable in his current form ahead of his side's meeting with Barcelona.

Messi has scored 51 goals in all competitions this season, and Guardiola, who won the Champions League twice with the Argentine during his time at the club, concedes that Bayern will find it difficult to stop him from having an impact on the first leg of the semi-final.

"There is no defence that can stop Messi. It is impossible," the Bayern boss told reporters. "How he is playing at the moment, you can not 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."

Messi revealed on Tuesday that he no longer has "any kind of relationship" with Guardiola.