United have opened the top tier of the East Stand for the first time in 12 months and will be boosted by a crowd in excess of 35,000.
Blackwell said in the Yorkshire Evening Post: "This is the biggest night we've had here since we played Valencia in the semi-finals of the Champions League five years ago.
"We had the game at Arsenal when we avoided relegation, but since we went down it's all about getting back in the Premier League and they don't come much bigger than the games we've got this weekend.
"Elland Road is one of the great footballing cathedrals and there is no better place to be when it's packed to the rafters.
"The players are excited. They are talking about the game and the size of the crowd. It means a lot to them to know that everyone is behind them. The players came here for nights like this.
"Steve McClaren asked the Middlesbrough fans to sing his side to the UEFA Cup final last week and they did. I hope our fans can sing us to the Premier League."