A Daniel Sturridge penalty and a Roberto Firmino strike gave the Reds a comfortable win last week, leaving them in firm control of the tie ahead of the return leg at Old Trafford on Thursday.
Rooney, though, believes that Louis van Gaal's men can turn the tie around in Manchester, though he will be forced to watch on from the sidelines having missed the previous eight games with a knee ligament injury.
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"Liverpool is going to be tough but two goals is doable," he told the Daily Mirror.
"We have good players and the first goal will be important. If we get that, then we will be back in the game."
United have struggled for form in recent weeks, failing to win any of their three previous fixtures.