Barcelona striker Luis Suarez has said whether Lionel Messi features in Saturday's Clasico is "a decision for the coach and for him" but believes "the feelings are very positive" that he will play at the Bernabeu
Messi has not featured for Barca since tearing a ligament in his left knee in September, but returned to full training during the international break.
Real Madrid Castilla coach Zinedine Zidane said the return of the fixture's all-time leading goal-scorer for the fixture would be "bad news" for Real -- but Suarez suggested it was very possible.
The Uruguay international told a news conference: "If he plays or not is the decision for the coach and for him. He is training with us and the feelings are very positive, but we must wait. It is an injury that can have risks for the future.
"We do not know if Leo would play from the start or be on the bench. It depends on how things go.
"He can change everything [in a game] at any moment. But he has been two months without playing."
If Barcelona win at the Bernabeu they will go six points clear of Real, but Suarez said it was much too early to talk about the title race.
"La Liga will not be finished by going six points ahead of Madrid in November," he said. "There will still be a lot of the championship to play -- you cannot think it could be over. Atletico [Madrid] are also there, and they will end up fighting for the title."
Madrid captain Sergio Ramos is likely to play after a pain-killing injection in his injured left shoulder, but Suarez said no player would look to target a fellow professional.
"I will not go to look for Sergio's shoulder, just as nobody will seek out Messi's leg," he added. "We are colleagues."
Asked about the likely whistles for Barca defender Gerard Pique from Madrid's fans during the game, ex-Liverpool star Suarez said his own experience was that such treatment only made people more determined.
"Pique is a special player and the whistles do not make sense," he said. "I was whistled in all English stadiums, many places, and it motivates you. You must set all that aside, focus on your team, and winning the points."
Spain's secretary of state for sport Miguel Cardenal has said security for Saturday's game will be heightened after last week's terror attacks in Paris but stressed that it is set to go on as scheduled.