AFP, Madrid : Barcelona and Real Madrid could be playing to be first in La Liga over the Christmas break on Wednesday but both are at risk of pre-Clasico defeats if their focus wavers this weekend. There are few tougher fixtures in the league than Barca’s away at free-flowing fourth-placed Real Sociedad on Saturday or Madrid’s trip on Sunday to a revived Valencia, who have won three games on the bounce and beat Ajax in Amsterdam to win their group in the Champions League. Already qualified in Europe, Barcelona and Real Madrid had the luxury of rotating key players in midweek but as the emphasis shifts towards their crunch meeting at Camp Nou, the danger is that they underestimate the tasks in front of them. Both have hit their stride in recent weeks, pulling away from the chasing pack while leaving behind early-season bumps that had placed the futures of their coaches in doubt. Barcelona have won 13 of their last 15 games and seven out of their last seven, a run that has coincided with the return to form and fitness of Lionel Messi, who has 14 goals and two hat-tricks in his last 11 matches. Madrid, meanwhile, have won nine out of their last 12, If their own surge has been slightly less consistent than Barca’s in terms of results, their performances have been more convincing. In their last 10 games, they have scored 28 goals and conceded only five. In normal circumstances, both might therefore have been expected to come away from Anoeta and Mestalla with victories but each have reason to be wary. Off the pitch, the threat of political unrest around the Clasico lingers, with Catalan independence demonstrations expected at Camp Nou both before and during the game next week. Barcelona president Josep Maria Bartomeu called for calm on Thursday and insisted the match would not be postponed again but, with families and friends in the city and likely to attend the game, it would be understandable if his players’ minds were not fully on football this weekend. Valencia and Real Sociedad are hardly opponents to be taken lightly either. Under Albert Celades, Valencia are showing signs of a resurgence, having won six out of their last eight, the two slips owing to a last-minute goal against Real Betis and a hatful of chances missed against Chelsea. At Mestalla, they have lost only once in their last five meetings with Real Madrid. Real Sociedad, meanwhile, have arguably been the most attractive team to watch in the division this season, even if their strong start has faded in recent weeks. They will also attack Barcelona, who have repeatedly been proven vulnerable against sides with pace and ambition on the break. A slip for either of the top two could play into the hands of Sevilla, who are at home to Villarreal on Sunday, or Atletico Madrid, who host Osasuna on Saturday, fresh from their morale-boosting win over Lokomotiv Moscow in the Champions League.