Cristiano Ronaldo is back on Portugal duty this week ahead of his country's crunch Euro 2016 qualifier clash against Serbia on Sunday night. Ronaldo was in the thick of the action at training following Real Madrid's 'El Clasico' defeat by Barcelona on Sunday night. The Catalans opened up a four-point lead over their arch rivals at the top of La Liga following their 2-1 victory at the Nou Camp. Cristiano Ronaldo (centre) takes on Ricardo Quaresma (left) and Vieirinha during training on Wednesday . Ronaldo has a chat with Portugul head coach Fernando Santos during the session in Lisbon . Ronaldo was waering his signature model Mercurial Superfly boots during the training session . The Los Blancos star will have to put that defeat to the back of his mind, however, as Fernando Santos' side gear up for the visit of Serbia. Ronaldo looked focused during his side's training session at their team base in Lisbon joining fellow team-mates Pepe, Ricardo Quaresma and Vieirinha. Portugal got their Group I campaign off to an awful start when they were lost 1-0 at home to Albania last September before bouncing back with a 1-0 victory against Denmark the following month. Portugal and Real Madrid centre back Pepe controls the ball as the Portugal coaching staff watch on . A narrow 1-0 win against Armenia in November has revived Portugal's Euro bid as they look to keep pace with the Danes at the summit of the group. Victory for Portugal on Sunday would stretch their gap over Serbia to eight points after four matches.
Portugal host Serbia in their Group I fixture in Lisbon on Sunday night . Denmark currently sit top of the Group on seven points . Victory for Portugal on Sunday would stretch their gap over Serbia to eight points after four matches .