UEFA Champions League holders Barcelona begin the defense of their title when they host debutants Levski on Tuesday in Group A that includes English champions Chelsea and Germany's Werder Bremen.

"I do not believe in favorites. You have to show you are the best on the pitch," Rijkaard was quoted as saying by Barca official website on Monday.

"I know that people consider us to be favorites, but that will not change our mentality," the Dutch coach added.

Rijkaard believes being favorites count for nothing, citing the Catalans' two UCL matches against Celtic and AC Milan in the past seasons as examples.

"When we drew with Celtic in Camp Nou (Barcelona venue) we were the favorites, and it was the other way round when we beat Milan in Camp and they were billed a favorites," he said.

Barcelona recovered from their 3-0 defeat to Sevilla in the European Super Cup as they opened their La Liga season with two successive victories.

Although the Spanish champions kept a clean sheet in their 3-0 win over Osasuna on Saturday, Rijkaard is worried after his side conceded two goals against Celta Vigo in the first match.

"We have to improve certain things that have cost us goals, the defense is not to blame because the whole team must help out in defending," he said.