Rovers set up the clash with victory over Watford in last night's replay.
Ahead of the clash at Prenton Park, Mellon was asked if United were vulnerable against lower league opposition, “No. They are a fantastic football club and will come here very professional. I've seen the other side of that when I was at Shrewsbury and they came like robots, did the job and got out of town. I know that is the threat they possess.
“We have to go out there and understand that is what will come here. They are an unbelievable football club and we are a League One club, at the bottom end of League One, but we are going to give it everything we've got. We will try to represent the club again and the players will run their socks off again and who knows?
“What we do know is that we will be up against a formidable outfit."
Mellon added: “A lot of hard work has gone into the pitch. We got it on and it was a good game on there. Nigel wouldn't moan about it because he's a good guy and he knows what it is like in the lower leagues.
“I don't think it's an opportunity because of the form United are in. I know they have a threat. We have to make sure we are ready. We will give it everything we have got. There is no doubt we will be up against a good side."