A narrow 1-0 win over Watford on Wednesday night boosted United's hopes of recovering what has been a disappointing Premier League campaign, with Van Gaal's men now level on points with fourth-placed Man City.
But the Dutchman is remaining cautious over his side's chances, telling reporters: "We go step by step. I think Liverpool are a nasty opponent. They won 3-0 against City, and that is not nothing.
"We have to go step by step, because we have four wins in four but we have a small selection. There are players coming back but I still have to solve a problem in my line-up every week.
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"I think you can see the statistics with how many players are injured, and then you can see how difficult it was and we are still in with a chance of being in the top four of the Premier League. That's not bad.
"And we're in the FA Cup quarter-final, and that's not bad. And we're still in the Europa League, and that's not bad. But we have still a full programme. We have played 40 games and still have so many to play. It's very difficult to fulfil the expectations."