Cristiano Ronaldo has scored nine goals in six games against Bayern Munich

Jerome Boateng says only a defensive team effort can prevent Cristiano Ronaldo adding to his tally of nine goals in six games against Bayern Munich on Wednesday.

Bayern host Real in a blockbuster Champions League semi-final first leg, at the Allianz Arena with Ronaldo in goalscoring form.

The Portugal superstar has scored 15 goals in the Champions League this season, hitting the net in each of Real's ten games in Europe.

"We can only stop Cristiano Ronaldo as a team," Bayern centre-back Boateng told German magazine Kicker.

"In front of goal, he's like a machine. You can't shut him out completely, he always gets his chances in a game, because of the lines he runs and his excellent timing.

"Real base their game around him and it's important we give him as little room as possible."

Jerome Boateng says Ronaldo is like a machine in front of goal

Ronaldo was at his lethal best when Real beat Bayern 6-3 on aggregate in last season's quarter-finals -- scoring five of their goals.

He hit two second-half goals as Real came from behind to win 2-1 in Munich, then scored a hat-trick in a 4-2 extra-time win in Madrid.

That came after he scored twice in Munich in the 2014 semi-final 4-0 rout of Bayern and hit two more against the Bavarians in the 2012 semis.

"There is a no more complete striker than Ronaldo. Left foot, right foot, header - he is in perfect control of everything he does," added Boateng.

"I went through only once against him with Bayern, but twice we have gone out. He also has the best team-mates at Real. Shutting him out is only 50 per cent of it, the other players are simply too good for that at this level."