"We lack the intensity that we used to show on the pitch. I'm sure that we'll play more intensively against Russia. It will be a very tough match against Russia because they are quite strong physically. They play a very fast tempo and have good forwards," Pereira told journalists.
The 34-year-old is Uruguay's most capped player, appearing in 125 matches for his country since his international debut in 2005.
Uruguay will face Russia in Samara on Monday in a match that will decide which of the teams wins Group A, while both have qualified for the round of 16.
The 2018 FIFA World Cup kicked off on June 14 and will continue until July 15, with the matches being played in 11 cities across Russia.