MADRID (AP) -- The biggest game of the year has arrived in Spain, filled with doubts over the presence of one of its biggest stars and surrounded by security concerns prompted by the attacks in Paris.
Real Madrid and Barcelona will play at Santiago Bernabeu Stadium on Saturday in the first clasico of the season.
Authorities are promising unprecedented security measures because of what happened in France last week, but it remains unclear whether Barcelona's Lionel Messi will be fit to play following a long injury layoff.
Messi returned to practice this week, nearly two months after tearing a ligament in his left knee, but the club is yet to say whether he will be available.
"Messi can change the game and he's done incredible things in previous clasicos," Barcelona striker Luis Suarez said. "But it depends on the doctors and what they think is best for him. He has looked good while training with us over the last few days but it's an injury that could take a sudden turn for the worse."
Messi is the all-time leading scorer in the clasico with 21. Cristiano Ronaldo, who has 15 goals, is guaranteed to start for Madrid.
Here are other things to watch for:
INCREASED SECURITY: Spanish authorities have declared the game a high-risk event and announced they will double the police presence at the Bernabeu.
Nearly 1,500 private security agents will be working during the game, and at least 1,000 national police officers.
Security zones will be implemented outside the stadium, keeping those without tickets or credentials away from the 81,000-capacity venue.
FIGHTING FOR THE LEAD: Barcelona has a three-point lead over Real Madrid going into the match, but a loss will drop the Catalan club to second in the standings on goal difference.
Madrid had been in front until its first loss of the season at Sevilla two weeks ago.
"I don't think we'll have won the league if we go six points ahead of them," Suarez said. "It's still too early to say who is going to win it. The league is going to be a long one, and Atletico (Madrid) will be up there, too, so this game won't decide anything."
Third-place Atletico, which plays at Real Betis on Sunday, is one point behind Madrid, and four behind Barcelona.
ATTACKING POWER: Suarez and Neymar have been carrying the load for Barcelona in Messi's absence. The South American duo have 20 of the team's 23 goals since Messi was injured.
Neymar scored five in the last three Barcelona games, while Suarez found the net three times.
Ronaldo has scored in each of the last three clasicos, and scored at least one in a clasico in the last five seasons.
Karim Benzema has also done well against Barcelona in recent years, especially when at the Santiago Bernabeu, where he's scored in the last four clasicos.
Real Madrid arrives with the league's best attack with 26 goals, one more than Barcelona.
INJURY WOES: Madrid should have back goalkeeper Keylor Navas, who has missed action since the beginning of the month because of a muscle injury.
Sergio Ramos, who has been nursing a shoulder injury, also should be fit. The defender has yet to miss a clasico, having started in all 20 of them in his career with Madrid.
Benzema was not 100 percent guaranteed to play after coming off a long layoff because of an injury and a sex tape controversy that led him to be briefly detained in France.
It remained unclear whether Barcelona would be able to count on midfielder Ivan Rakitic, who has been recovering from a muscle injury.
WORLDWIDE ATTENTION: The Spanish league said the clasico will be broadcast on large screens in Dubai, Shanghai, Miami, and a Spanish military base in Lebanon. The league organized the events abroad as part of its push to expand the brand internationally.
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