The 24-year-old, who was booked for simulation during Barca's 2-2 draw with Real Sociedad last month, was denied a penalty kick following a challenge from Alberto Botia in last night's match with Sporting Gijon.
Many pundits suggested that Messi went down under the tackle too easily, but Guardiola has insisted that his player was fouled.
"I did not see it, but everyone should know that when Messi goes down it is because he has been fouled," the manager told reporters after the match. "The officials saw it better than me, you should know that."
Barca won the match 1-0 courtesy of an early goal from Adriano.