The Rayo boss believes that his Vallecas outfit can stop the Argentina international, but he is also concerned about the Catalans' other decisive players
Jemez has admitted that the Argentine is arguably one of the best players in the world, but believes the prolific forward is by no means the Blaugrana's only attacking threat as they have a number of players who can decide a match.
"What worries me most about Barca is their strength as a unit. It would appear that Messi is the player that you need to focus all your attention on, and of course, he is one of the best in the world," Jemez was quoted as saying by AS.
"However, Barcelona have a whole number of players who can win a game at any moment. Focusing on just one player won't do you any good.
"You have to be wary of everything, above all the small details, so you can counter a team, not just Messi. Even though we know how to stop him, Barcelona are more than just Messi.
"Pedro, for example, is the fastest player I have ever seen."
Saturday's match is scheduled to kick off at 22:00CET.