The Brazilian defender believes his side can still win the league title.
And the 24-year-old thinks United can climb to second in the table within three games.
Louis van Gaal's side travel to West Brom next Monday, before facing league-leaders Chelsea and then second-placed Manchester City.
If they win all three, the defender believes they will move to second.
"If we start to understand the way of playing, like we are doing, and when the results are positive, everything starts to run smoothly and for sure we have chances to win the title," Rafael told Perform.
"We will have three difficult games - against West Brom away, after this we face Chelsea, the actual leader, and then Manchester City in their stadium. These games will be very important for us.
"Against West Brom we need to be very focused as they are showing good performances, then we face Chelsea at home and City.
"We need to think about these three games and if we win we will be close to the leader, probably in second place, so we need to be positive and try to win these three matches."
After seven Premier League games, Man United are currently fourth in the standings, despite a slow start to the campaign.