Cristiano Ronaldo was put through his paces during a Portugal training session as they prepare to face Serbia in a crunch Euro 2016 qualifier on Sunday. Portugal host their European rivals knowing a victory would stretch the gap over Serbia to eight points after four matches. Despite the importance of the tie, with Denmark currently sitting top of Group I with seven points, Ronaldo and his team-mates seemed in good spirits. Cristiano Ronaldo (right) was put through his paces by manager Fernando Santos during Portugal training . Ronaldo (left) smiles with Portugal team-mates including Real Madrid defender Pepe (middle) The Real Madrid striker has been in fine form for his club this year and has scored an impressive 31 La Liga goals in 25 matches. However, the former Manchester United player will be aiming to put last Sunday's El Clasico defeat by Barcelona behind him. Ronaldo was on the scoresheet at the Nou Camp when he equalised after Jeremy Mathieu had opened the scoring but Luis Suarez's winner secured a 2-1 victory for Barcelona. The Los Blancos star has scored 31 La Liga goals in 25 matches this season for his club . The 30-year-old seemed in high spirits during training despite the importance of Sunday's clash with Serbia . Portugal have endured an indifferent Euro 2016 qualifying campaign so far after losing their opening fixture at home against Albania. But victories against Denmark and Armenia leaves them in second spot and a win on Sunday would stretch their gap over Serbia to eight points after four matches. Ronaldo takes a break from training with Fabio Coentrao (centre)
Portugal face Serbia on Sunday in crucial Euro 2016 Group I clash . Victory for Portugal would see them move up to nine points . Cristiano Ronaldo has scored 31 La Liga goals in 25 matches this season . READ: Ronaldo back in action for Portugal ahead of Euro 2016 qualifier . WATCH: Ronaldo pranks Portugal team-mate Ricardo Quaresma .