The Reds play the second leg of their Carling Cup semi-final against City at Anfield on Wednesday, before facing United in an explosive FA Cup fourth round tie the following weekend.
However, Liverpool currently sit in seventh place in the league, five points behind Chelsea in the chase for fourth and a spot in the UEFA Champions League next season.
As a result, Reina has picked out Saturday's Barclays Premier League trip to Bolton as the team's most important match out of the next three games.
"It definitely won't be difficult to put those games to the back of our minds because the first game is Bolton and is therefore the most important of all three," Reina told Liverpoolfc.tv.
"After that, we know how huge it is to play a Carling Cup semi-final, second leg at home and everybody knows how big the tie against Manchester United is going to be.
"It is an important game at Bolton. It is vital for us, we have to get some momentum going and keep winning games. It's important not to lose - but it's even bigger to win the games and get three points after three points."
Kenny Dalglish's side were held to a goalless draw with Stoke at Anfield in their last Premier League match which the Spaniard admits proved to be a highly frustrating experience for him.
"It's always frustrating when you don't win at home," Reina said.
"But that has been the case so many times this season and it is disappointing because we want to win.
"The possession doesn't mean anything. Sometimes the team who has the ball the most doesn't end up winning. All that we want is to score one more goal than our opponents.
"Sometimes when you are creating those opportunities, it is easy to stay cool and calm - but when the opportunities don't come along, it is difficult to explain why.
"I wouldn't say our away form has been excellent, it could have been better, but it's been pretty good.
"I think the level of concentration and focus in every game has been excellent."