Cristiano Ronaldo, Gareth Bale and Karim Benzema were once the untouchable trio, but only one of Real Madrid's feted "BBC" can be sure of their place against Bayern Munich on Wednesday and ahead of the mouth-watering fixture, Bayern’s Jerome Boateng brands Ronaldo as a machine.

Ronaldo has dragged Real into the Champions League semi-finals with, even by his standards, an astonishing goal glut that includes 22 in 12 games, and at least one in each of his last 11 matches in Europe.

"It's impossible to completely stifle Ronaldo, we can only stop him as a team," Bayern defender Jerome Boateng said on Monday.

"An attacker can not be more complete than him -- left foot, right foot, head, he controls everything and in front of the goal, he's a machine".

But while Ronaldo has enjoyed a fresh spurt in his new role of predatorial centre-forward, his two partners have found their responsiblities reduced ahead of the first leg at the Allianz Arena.

Bale's decline began first. After returning from injury earlier this year, he was on the bench for both legs against Paris Saint-Germain and the first leg against Juventus.

In the second leg, he did start, only to endure the humiliation of being taken off at half-time.

Benzema's fall has been more surprising given the striker had been Zinedine Zidane's preferred partner for Ronaldo, his work rate and supply highly valued despite the Frenchman's lack of goals.

But Benzema's link-up play has slackened, thrusting that dry patch -- one goal in 10 games and only four in 24 -- more clearly into view.

A little blip

"He does suffer a little bit, when he misses chances he suffers but the solution is easy," Zidane said. "He has to keep working. It is just a little blip he is in at the moment."

Bale and Benzema's dip has coincided with Ronaldo's golden run, a parallel that may not be entirely coincidental.

Ronaldo in a Real team centred on playing to his strengths is nothing new, but as the Portugese has grown narrower in his scope, perhaps his team-mates have had to sharpen their focus in providing service to him.

Zidane has often deployed 4-4-2 in the biggest games this season, with Lucas Vazquez and Marco Asensio preferred on the flanks for their defensive discipline and willingness to send crosses into the box.

Bale is not viewed as conscientious enough in the wide midfielder role while Benzema's key selling point was his link-up play. When that broke down, his appeal diminished.

"I don't see anyone looking sad," Zidane said. "I said to the pair of them the other day, they would both like to score more goals but everyone is working well.

"It is always going to happen in a side like ours, there are players in good form and in the team and playing well."

Even if Isco is selected, it means Real are likely to line up with one of their more modest-looking attacks for a crunch Champions League tie.

"I'm not worried," Zidane said last week. "It's true that in the last two games we have had chances and we have not taken them but now we are going to have a game on Wednesday away from home.

"We are going to try to score and what we have to do is to think positively and realise that this is football anything can happen, no matter who is playing on the pitch."

Real travel to the Allianz Arena on Wednesday for the first leg with the return leg in Madrid to be played on May 1.