The Uruguayan striker said Wednesday that Messi has looked sharp in training after returning from a long injury layoff, but it remains unclear if doctors will clear the Argentine playmaker for Saturday's match at the Santiago Bernabeu stadium.
Messi began training again this week, nearly two months after tearing a ligament in his left knee in a Spanish league game.
"It depends on the doctors and what they think is best for him," Suarez said. "He has looked good while training with us over the last few days but it's an injury that could take a sudden turn for the worse."
Messi, the all-time leading scorer in the "clasico" with 21 goals, missed nine matches since the Sept. 26 injury against Las Palmas at the Camp Nou.
"Messi makes all the difference, but we'll have to wait and see whether he starts or perhaps comes on later," Suarez said. "At the Calderon he showed that he can come on for just twenty minutes and get you the three points."
Messi came off the bench to rally Barcelona to a 2-1 win at Atletico Madrid's Vicente Calderon stadium earlier this season. He had been named as a substitute after missing training to be at the birth of his second son in the week leading up to the Atletico game.
Suarez and Brazilian striker Neymar have been carrying the load for Barcelona in Messi's absence. They have scored 20 of the team's 23 goals since Messi got injured.
"I'm going into the game on form and happy that the team is playing so well," the Uruguayan said. "We want to win this match and end it as well as possible."
Barcelona leads the Spanish league after 11 rounds. It has a three-point lead over second-place Real Madrid and needs at least a draw on Saturday to remain atop the standings. A loss would see Madrid return to first place courtesy of a better goal difference.
In Wednesday's press conference, Suarez also said that playing the "clasico" is every player's dream.
"It's such an important occasion," he said. "When you appear in a 'clasico' it feels that you're living a dream that every footballer aspires to."
He added: "I remember watching the 'clasico' on TV and seeing (former Barcelona star playmaker) Ronaldinho score. They're great games where you see lots of good football. When you are out on the pitch you feel like you're living every footballer's dream."
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