A key cog of the Real Madrid machine is ailing ahead of the crucial Champions League second leg encounter with Paris Saint Germain.

Livewire left-back Marcelo pulled up in the first half of Sunday's clash against Betis, clutching his thigh. He was immediately substituted, with Madrid releasing a statement later stating it was a hamstring injury. Croatian midfielder Luke Modric is also carrying a similar knock, and both face a Race Against Time to be fit in time for the PSG game in two weeks.

Race Against Time

Marcelo was one of the first leg's star performers, even notching the all-important third goal which sees Madrid take a two-goal cushion to Paris.

A dynamic force down the left-hand flank, Marcelo is the quintessential Brazilian left-back if ever there was one, offering overlaps, darting runs and penetrative passes like a left-winger. A popular figure at the Bernabéu, the 29-year-old has racked up over 300 appearances for the Spanish juggernaut since he signed in 2007 at the ripe old age of 19.

That same year saw the departure of imperial compatriot Roberto Carlos, and Marcelo soon snatched the left-back spot as his own. He hasn't looked back since, and it would be a huge loss to Zidane's side should he be ruled out for the second leg. Hamstrings generally don't heal within two weeks, but early reports suggest he may have a chance to make it, although we won't know until closer to the time. His injury history is relatively clean, too, so a speedy recovery isn't out of the question.

Neymar Awaits Galacticos in Paris

The clash in Paris is undoubtedly Madrid's biggest of the season. Shockingly dumped out of the Copa Del Rey by Leganés at the Bernabéu, and languishing fourteen points behind Barcelona in La Liga, it's all they have left to play for [VIDEO]. Zidane has faced the full brunt of the unrivaled pressure that comes with being an underperforming Real Madrid manager [VIDEO], even if he has stocked the trophy cabinet quite nicely since he took over from Rafa Benitez the season before last. Cristiano Ronaldo is now 33 and has seemingly taken a step back this season. Karim Benzema has also come under fire.

Meanwhile, Gareth Bale has yet to step up to the limelight as the star is amongst omnipresent injury niggles. One fears a changing of the guard could be in store in the Spanish capital, should they succumb to PSG in the second leg. A fit Marcelo would certainly help to ease those concerns as Neymar and co. are ready to pounce.