Argentina fell to a shock 2-1 defeat to Saudi Arabia on Tuesday and need a victory against Mexico to keep their World Cup campaign on track. Scaloni said Messi, 35, trained with the rest of the team on Thursday and is ready for the challenge on Saturday.
"He's feeling well but more than ever we need everyone," Scaloni said. "We have no questions over [Messi's] physical level, and emotionally he's feeling well so no problems there."
He added: "Leo is doing well, as our his other teammates. We know tomorrow we have an important match and most young players know that everything will be left on the pitch. Everything depends on us -- that's why we need to give everything on the pitch."
Scaloni said he will not rip up his Argentina blueprint after the shock defeat. "You need to rise up after a blow like that, bounce back together and think of the upcoming match -- that's all you can do," he said. "For a long time everything was perfect for us -- all joy -- but in difficult moments we need everyone's support.
"This group is ready to rise and bounce back, we have no questions over that in that regard of how we play the game. With all the responsibility -- we know there's a whole country behind us -- but everyone on the pitch will break our backs until the last second we are on the pitch so we can reverse the opening match."
Striker Lautaro Martinez said the opening defeat was a "hard blow" but the team is ready to bounce back. "Tomorrow's match will be like a final as we need to win," Martinez said.
"It'll be an important match for our future, not only in terms of pecking order but in terms of what we will manage to do on the pitch. We've proven that we have the players and the quality. We are eager and ready and eager to square up against the next opponent."
Martinez and Scaloni spoke to the press on the two-year anniversary of Diego Maradona's death and Argentina are focused on delivering a performance fit to honour the 1986 World Cup winner.
"It's a very sad day for everyone, really," Scaloni said. "Tomorrow we will hope to bring some joy for Maradona if he's looking at us from the sky.
"That's the most important thing for us. Every time we're reminded of him, it's unbelievable that he's not here with us, so it's a sad day for us. Hopefully tomorrow will be a happy day for all of us."