Real Madrid's Cristiano Ronaldo (left) is helped off the field after suffering an injury during the El Classico on Sunday. Pic/AFP

Zinedine Zidane refused to put a time frame on Cristiano Ronaldo's injury absence after the forward had to be substituted at half-time in an entertaining 2-2 draw against Barcelona. Ronaldo had cancelled out Luis Suarez's opener for the unbeaten La Liga champions, but picked up an ankle knock while tapping in Karim Benzema's header back across goal from Toni Kroos' cross.