El Clasico 2015: Lionel Messi, Cristiano Ronaldo and Key Players at Camp Nou

Barcelona and Real Madrid's perennial rivalry resumes once more on Sunday in El Clasico, the always-eventful game where the two best players in the world, Lionel Messi and Cristiano Ronaldo, are pitted directly against one another.

The titanic clash is arguably the second-biggest match in club football after the UEFA Champions League final, and last time around it hit viewing figures of 400 to 500 million, per BBC Sport. This time, it has the added intrigue of being a potential title-decider.

As Spanish football writer Sergi Dominguez points out, Barcelona enter the game in superior form:

Barcelona enter the game just one point ahead of their arch rivals, but a win would see them four points clear with 10 games remaining. Hardly an insurmountable lead, but with a team that drops as few points as Barca, four points is a lot to overcome.

Likewise, Real can put themselves back in the driver's seat if they claim victory. The possible permutations relating to Sunday's clash and the two teams' league head-to-head record are summed up thusly:

Below we take a look at how Messi and Ronaldo stack up against each other, and who else could prove a key figure in El Clasico.

Messi vs. Ronaldo

When it comes to the statistics, Messi has a slight edge over his long-time rival in both goals and assists for the season.

Per WhoScored.com, Messi has 43 goals and 16 assists in all competitions this season, compared with Ronaldo's 39 goals and 13 assists.

It is Messi who comes out on top in El Clasicos as well. The diminutive star is the all-time leading scorer in El Clasico with 21 goals, and he has also contributed 12 assists in his 29 appearances against Real, per messivsronaldo.net.

Ronaldo trails his rival with 14 goals and a solitary assist. 

Messi is also on the verge of a landmark, according to Sergi Dominguez:

Barcelona legend Hristo Stoichkov has added fuel to the fire by suggesting three-time Ballon d'Or winner Ronaldo does not enjoy the constant comparisons with his rival:

If Ronaldo wants to make the comparisons more favourable, a decisive performance is needed from him. By his own standards, the Portuguese superstar has had a relatively poor time of late.

As Sky Sports' Guillem Balague notes, Madrid have not been taking chances with their usual consummate ease in recent weeks. Against Barcelona, Real's sharpness and intensity needs to return, and that starts with Los Blancos' biggest star: Ronaldo.

Key Players

Ivan Rakitic

With Andres Iniesta failing to score or create a single league goal this season, per WhoScored.com, and Xavi now 35 years old, Barcelona's creative responsibilities in midfield fall largely on Rakitic's shoulders.

In this regard, the Croatian has not disappointed, scoring five goals and assisting six in all competitions, per WhoScored.com.

The 27-year-old's ability to create chances for his team-mates and provide energy in the engine room is highly impressive, as the video below demonstrates:

With Real's midfield geared heavily towards going forward and lacking a strong defensive-minded figure, Rakitic can exploit the space between their midfield and back four, providing Messi, Neymar and Luis Suarez with plenty of ammo.

If Real hope to come away from the game with a win, they would do well to limit the playmaker's time and space with the ball.

Luka Modric

Modric is only two games into his return from a thigh injury, but he could prove key in El Clasico on Sunday.

The Guardian's Sid Lowe believes his comeback to be a positive step for Real, one of few others in recent weeks:

As Bleacher Report's own Aleksandar Holiga notes, Modric has been a crucial figure in the evolution of Real's style under Carlo Ancelotti, enabling a more balanced, patient and fluid manner of play to develop as an alternative to the fast-paced counter-attack Los Blancos are so famous for.

Modric's comfort in possession can help Madrid keep the ball and force Barcelona to do more of the running, though winning the ball off them in the first place may prove challenging.

With Barca likely to retain plenty of possession, Modric's ability to cover space will be vital on Sunday.

Competition	Matches Played	Real Madrid Wins	Draws	Barcelona Wins
La Liga	169	71 (42%)	32 (19%)	66 (39%)
Champions League	8	3 (38%)	3 (38%)	2 (25%)
Copa del Rey	33	12 (36%)	7 (21%)	14 (42%)
Spanish Super Cup	12	6 (50%)	2 (17%)	4 (33%)
League Cup	6	0 (0%)	4 (67%)	2 (33%)
Total	228	92 (40%)	48 (21%)	88 (39%)

Against Barca's strong team unit it will be fascinating to see how far along in his recovery he is. Any lack of fitness could prove a significant factor in how the match plays out. 

If Modric is unable to offer his usual defensive contribution, Barca will have the space to run riot. Expect Messi, Rakitic and Co. to exploit any spaces in behind the Madrid man.