The Spanish outfit open their European campaign next Tuesday against Shakhtar Donetsk, but Prieto has called for focus ahead of their league trip to Levante this weekend.
"We are clear that Saturday's game comes first, we have started preparing for it from today. It will a tough game against an opponent that since we have returned to the Primera Division [in 2010] we have not beaten and they now have a new coach," he told reporters at a press conference.
"They have four points and their only defeat was against Barca, so we have enough reasons to worry. Ciutat de Valencia is a tough ground and they are a tough team, while [coach Joaquin] Caparros can be very elaborate, and so this will not be different from previous years. We will see if we can change the course of the last few seasons, though."
Sociedad have taken four points from their first three games this season.