Old foes Barcelona and Chelsea get ready for another showdown when they do battle in the Champions League round of 16 on Tuesday night.

Playing time, form, hold-up play and an aerial threat may put Olivier Giroud ahead of Alvaro Morata for this one. Marcos Alonso returns from injury while Tiemoue Bakayoko, David Luiz and Ross Barkley are all doubts.

Philippe Coutinho is ineligible as he is cup tied. Ousmane Dembele makes the trip but may only start on the bench. Nelson Semedo is suspended for the visitors while Thomas Vermaelen is included in the squad despite injury concerns.

Here, we look at some of the key talking points ahead of the encounter.

EDEN HAZARD HAS A BIG PART TO PLAY

Whether he likes it or not, Eden Hazard will be measured against Lionel Messi when Chelsea and Barcelona clash. Like the Argentine, his incredible dribbling ability, creativity, acceleration and low centre of gravity sets him apart and makes him a lethal attacking force.

He also enjoys a free role in behind the main striker from where he can be heavily involved in build-up play but also in a position to get on the end of chances in and around the penalty area.

With 15 goals and eight assists this season, his new role brings out the best in him. Gerard Pique and Samuel Umtiti’s communication and understanding will have to be spot on to keep tabs of his darting runs.

His ability to break away on the counter-attack could be devastating.

LIONEL MESSI – THE PLAYMAKER

Albeit in a different system, Messi is afforded a similar role to Hazard’s. The Barcelona star plays off front man Luis Suarez and is granted the freedom to roam. The Argentine may have to contend with special attention from the opposition – nothing he isn’t used to.

The industrious N’Golo Kante will be the deepest midfielder for the Blues and is likely to watch Messi like a hawk although a man-marking job would be ill-advised because he often drops so deep that the two full-backs are well ahead of him. Like his defence-splitting pass for Suarez’s opener against Eibar proved, he doesn’t need to score to hurt you.

If the likes of Messi and Suarez can isolate Chelsea’s centre-backs in one-on-one situations, they will have the beating of them and cause problems. But the Argentine’s influence has evolved beyond just running at defenders and scoring goals.

After Xavi’s departure and with Andres Iniesta in the twilight of his career, Messi has assumed the role of chief playmaker.

CHELSEA MUST COME ALIVE IN THE TRANSITION

For Chelsea, it’s all about the turnover. When Barcelona are without possession, they’re set up as a compact unit with two banks of four that are not easily broken down. Of course, every team is more vulnerable in the transition when they lose the ball, but Barcelona more so than others.

Their four-man midfield usually comprises of all central midfielders, outnumbering the opposition in the middle and relying on their full-backs to provide the width, but crucially leaving them open to the counter.

They throw so many bodies forward in attack that an early ball over the top can be their undoing and in fact has been on occasion this season. That’s precisely why Cesc Fabregas’ inclusion could be absolutely key.