Robertos companions were unable to defeat their host Cadiz on Thursday, to be held to a goalless draw in the local championship.
After the match, Roberto told Movistar: “We have to win the league.”
“It will not be enough for us to occupy a position in the top four, we have to fight for the title,” he added.
“I don’t think other teams have a list of better players than us,” he concluded.
Barcelonas new stumble made it eighth in the Spanish league standings, with only 9 points after playing 5 games.
Barcelona will host Levante on Saturday in the seventh round of the league.
Then he heads to Portugal to face Benfica in the second round of the group stage of the Champions League.
After that, a fiery confrontation awaits him in the capital against Atletico Madrid, the champions of the league.