Eden Hazard or Diego Costa: Who Will Be Most Important for Chelsea vs. PSG?

Paris Saint-Germain have long been admirers of Eden Hazard. 

As recently as last month the Ligue 1 champions were being linked with the Belgian by Le Parisien (per Sky Sports) and it's sparked all sorts of speculation about his Chelsea future.

For the sake of their UEFA Champions League ambitions this season, PSG must temporarily drop their Hazard infatuation; they will be better off paying more attention to Diego Costa.

The two sides meet in the second leg of their last-16 clash at Stamford Bridge on Wednesday and the tie is finely balanced. Laurent Blanc's men have a 2-1 advantage after their victory at Parc des Princes three weeks ago, but with an away goal to their name, Chelsea are feeling buoyed.

They have every reason to. Since Guus Hiddink replaced Jose Mourinho in December, the Blues have gradually restored their confidence and built some momentum as we approach the final stages of the campaign.

Hiddink's desire to shore things up defensively has been a big help, yet without Costa's goals, Chelsea would still be struggling at the wrong end of the table.

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The Spain international has rediscovered his menace in front of goal and looks like the player we saw last season when Chelsea were rampant on their way to lifting the Premier League title.

He really has stepped up, scoring nine goals in 14 appearances. Quite what has brought about this return to form, we can only speculate, but Costa's focus has switched from scrapping with opponents to scoring goals, and it's been the catalyst to Chelsea losing just once since December.

Of course, that defeat came against PSG when Costa had his chances to punish Blanc's men for some slack defending. In the first half of that game he saw a header tipped onto the crossbar by goalkeeper Kevin Trapp, who also denied him when one-on-one in the second period.

Costa remained a livewire, however. He was making things happen and in the three games he has played since, he has maintained his scoring streak.

Meanwhile Hazard has continued to disappoint. The Belgian has been a shadow of the player who swept the board of personal accolades last season and despite flashes of brilliance, it's clear he is still struggling.

The speculation over his future hasn't helped, nor has an apparent lack of sharpness and confidence. Hazard doesn't seem to have that burst of pace to get past defenders and when he finds himself in the final third, doesn't have the belief of old to carve out openings.

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He's among the biggest names in Europe, but facing PSG in such a crunch Champions League encounter has probably come too soon for him as he attempts to rebuild his season.

Whereas Costa has effortlessly flicked a switch, Hazard continues to toil and is suffering with the expectation that comes when the spotlight is on him.

It's matches like this Champions League clash when we're expecting him to come alive. So much of what Chelsea have achieved in recent seasons has been largely down to his brilliance, so when he's not delivering, it increases the pressure even more so.

Hazard has been the Blues' match-winner, but right now he's merely a passenger in their recovery. The expectation was that as this team got back to a high level, he would follow. It simply hasn't happened.

The Stamford Bridge talisman now is Costa. He's scored a third of the goals Chelsea have under Hiddink and has been their only consistent goal threat in that time.

What's more, Costa's form at home has been excellent, with the striker scoring seven times in seven matches since Hiddink's return as interim manager.

In five of those games, Costa has either scored Chelsea's opening goal or the winner, which outlines just how effective he has been.

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Whenever Chelsea need that inspiration, Costa is delivering. He's carrying his teammates.

PSG need to be wary of that. While Costa's Champions League record is poor in comparison to what we've seen domestically—his strike against Maccabi Tel Aviv way back in September remains his only European goal in Chelsea colours for two seasons—his form dictates an improvement.

If Chelsea are to overturn that 2-1 deficit, it's Costa who will do it. There isn't a more important player at Stamford Bridge right now.

Garry Hayes is Bleacher Report's lead Chelsea correspondent. All quotes were obtained firsthand unless otherwise noted. Follow him on Twitter @garryhayes.