Howard told BBC Berkshire: "You know when you come off that pitch you're going to be physically tired because they're going to push you 100%.
"Sheffield United play in your face, even if they're a goal down. They come back at you and they never give up."
He added: "It's going to be an extremely difficult game - totally different to the ones we've had of late against some good footballing teams. This one's going to be a real battle."
Howard was on the bench for Reading's 1-0 Cup win against Burnley last weekend and said the Cup run is lifting the whole squad.
"The boys are buzzing after the weekend. We were the better side and deserved the win.
"To knock two Premiership teams out of the Cup shows that we've some top class players down here. But in the league, we're in a bit of trouble and desperately need some points.
"There's a little less pressure [in the FA Cup]. You got out there and do the job and express yourself. We're not expected to win against the Premiership sides. It's all about confidence and hopefully we can take that into the league."
Sheffield United v Reading kicks off at 1945 on Tuesday 26 January and is live on BBC Radio Berkshire.
Source: BBC Sport