Simple question tonight then, should Real Madrid be worried about Cristiano Ronaldo's form, or is this just a blip? Can he rediscover his goalscoring touch tonight?

With Real's results also suffering in 2015, is an out-of-form Ronaldo a liability to the Spanish side? Or should he always play when available?

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No surprise to see Gareth Bale, Cristiano Ronaldo and Karim Benzema all start. Pepe returns after a month out with a rib injury while Lucas Silva makes his full debut.

Real Madrid XI: Casillas; Carvajal, Varane, Pepe, Marcelo; Kroos, Lucas Silva, Isco; Bale, Ronaldo, Benzema.

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Former Real Madrid coach Fabio Capello is more concerned, however, and believes Cristiano Ronaldo's form is having an impact on Real's overall performances and results.

They have lost to Valencia and Atletico Madrid this year, and also exited the Copa del Rey.

"It is very important that he is not at his usual level," Capello said., external "At the end of last year Madrid began the game already 1-0 ahead, because they had Cristiano. But he is an extraordinary player and we will return to 100 percent very soon."

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Real Madrid boss Carlo Ancelotti is not concerned about Cristiano Ronaldo's mini goal drought.

The world footballer of the year's last goal was one month ago, when he scored twice against Getafe. Since then, he has drawn blanks in La Liga games against Cordoba, Atletico Madrid and Deportivo.

Ronaldo has been struggling with a knee problem, but Ancelotti is confident he will be soon back to his best: "I think he's improving. He's not got goals but I think he has a good opportunity to do it against Schalke."

Also in Champions League action tonight are Porto, with the two-time competition winners travelling to Switzerland to play Basel.

Porto went through the entire group stage without a defeat, and in fact have lost just one of their 14 European games at home and abroad - highlighting the size of the task ahead for Basel, who have never reached the Champions League quarter-finals...

So can Cristiano Ronaldo get back on the goal trail in tonight's Champions League last-16 game?

It is as good a time as any, with Real Madrid having recorded an emphatic victory against Schalke in last year's Champions League on their way to the title.

They won 6-1 in Germany at the same stage of the competition last year, with Ronaldo helping himself to two goals, before a 3-1 win in the return leg sealed a 9-2 aggregate victory.

In fact, Ronaldo was virtually unplayable in that first leg, having 10 shots on goal in total - the same number as the entire Schalke team.

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Look at that stat, just look at it. Fifty seven goals in 57 Champions League games for Real Madrid, surely a ridiculous notion to suggest he is out of form?

However, no goals in his last three games is his worst scoreless run all season. In fact, he has managed just four goals in his last 10 appearances, a big contrast to the 17 he bagged in his first 11 matches of the season. Even, Darren Bent is in better form that the current world player of the year.

Make no mistake, in terms of the incredible level that Ronaldo performs at, this is not a great spell for the Portuguese forward...

Image source, Getty Images

Whether it is Arsenal and Tottenham sharing a ground or Lionel Messi turning out for Accrington Stanley, there are some things that you can be pretty certain about never happening in football.

Another, is Cristiano Ronaldo having a bad run of form.

But, and whisper it quietly, it seems poor Ronnie is going through a bit of a sticky patch.

Can he rediscover his goalscoring touch against Schalke in the Champions League tonight?