Key battles: Borussia Dortmund v Real Madrid

Cristiano Ronaldo always poses a threat for Real Madrid. Photo: PA

As Borussia Dortmund and Real Madrid prepare to do battle in the first leg of their Champions League semi-final tomorrow night, we look at the clashes that could decide which team emerges victorious.

CRISTIANO RONALDO v NEVEN SUBOTIC

The biggest threat to Dortmund needs no introduction. Cristiano Ronaldo may be overshadowed in Spanish and world football by Lionel Messi but his statistics are equally astonishing.

This season he has scored 46 goals in 45 matches for Madrid, 11 in 10 in the Champions League, and averages more than a goal a game in his career with the Primera Division giants.

Ronaldo's threat may start on the wing but it is through the middle where he can most hurt Dortmund, and there he will come up against Serbia international Neven Subotic.

The 24-year-old has been one of the most impressive defenders in German football over the past five years and has been linked with Chelsea and Manchester City.

MARIO GOTZE v XABI ALONSO

Dortmund will have to put the disappointment behind them of today's announcement that star midfielder Mario Gotze is to leave the club in the summer to join Bayern Munich.

The German champions will meet the release clause believed to be 37million euros, making the 20-year-old playmaker the most expensive German player in history.

There has long been hype around Gotze, whose importance to Dortmund is both as creator and goalscorer.The string-puller for Madrid is former Liverpool midfielder Xabi Alonso, whose passing from deep is such an important feature of Jose Mourinho's side.

Indeed, Alonso's value was highlighted in the last-16 clash with Manchester United at Old Trafford when he was superbly marked by Danny Welbeck until Nani's red card freed the Spaniard up to take control of the game.

JAKUB BLASZCZYKOWSKI v FABIO COENTRAO

Right winger Jakub Blaszczykowski has long been one of Dortmund's most influential players.

The Poland captain loves to cut inside and unleash fierce shots from outside the box and last summer made the 32-man UEFA long list as one of the best players in Europe.

Also on that list was Real Madrid left-back Fabio Coentrao, whose prowess as an attacking full-back means Blaszczykowski will have to spend time tracking back.

Mourinho has used the Portugal international solely for Champions League games in recent weeks, meaning he should have plenty of energy for forays down the left.