The Brazil international told the club's website: "When you play for a big team you have to take it game by game. Tuesday was a very important win for us because we wanted to stay in the Champions League, but we want to win the Premier League as well.
"Mathematically it's still possible but every game in the Premier League is difficult, as it will be on Sunday. Swansea are tough opponents and we've seen in the last few seasons, every time we go there it's a difficult game. We need to try to do our best and win the match.
"It's still possible to win the league, so come on, let's enjoy the position we are in and believe, like we did against Paris Saint-Germain. We need to have faith because we can still do it."
Chelsea currently sit second in the table, two points behind leaders Liverpool.