United have slumped to back-to-back defeats at Old Trafford against Everton and Newcastle in the last six days.
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The Premier League champions are down in ninth place in the Premier League, 13 points adrift of leaders Arsenal.
However, David Moyes' side have already qualified for the last 16 of the Champions League and they can secure top spot with a point at home to nearest rivals Shakhtar.
Rafael knows they can ill afford to feel sorry for themselves and the Brazil right-back has stressed the importance of finishing off the job against the Ukrainian champions.
He told MUTV: "It's very important we get back to winning at Old Trafford.
"It's our home and we have to play well here for our supporters. We should do this on Tuesday.
"Of course, everyone is disappointed with the results (against Everton and Newcastle) and the way we played. Now we must bounce back and try to get the wins again.
"It's important to win the group. We were a bit unlucky last season (to be drawn with Real Madrid) but it's always important to get first place.
"The Champions League is special. Ever since I came, I think it is special all the time for Brazilians."