When Madrid swept a crisis-ridden Barca aside 5-1 in the Spanish Super Cup last month, Zidane's men were expected to romp to the title.
The left-back suffered the injury during Madrid's shock 1-0 loss at home to Real Betis in LaLiga on Wednesday.
The former Betis midfielder kick-started his Real career with a two-goal brace on his LaLiga debut for the capital club.
"I am happy for (Ceballos)".
"There is no explanation as to why we haven't been able to score goals", he continued. "He showed that he has a place on this team".
However, Alaves got the equalizer and their first goal of the season in the 40th minute through their captain Manu Garcia. His powerful header from a cross by Munir El Haddadi was the Basque Country club's first goal of the season.
But Madrid responded three minutes later as Ronaldo broke down the right wing, took a shot which Alaves goalkeeper Pacheco fumbled, leaving Ceballos to fire a curling effort towards goal which flies into the bottom corner for his second of the night.
Ceballos caught Madrid's eye in the offseason after he was named the best player at the Under-21 European Championship, where he helped Spain reach the final before losing to Germany 1-0.
Ramos has been an integral part of Real Madrid since joining the La Liga giants from his boyhood club Sevilla in 2005.
But with his side already seven points behind early league leaders Barcelona and in desperate need of points, Zinedine will put his job over family ties.