The Latics are looking to bag a spot in the FA Cup third round for the first time since 2021.
The Oldham boss comes toe-to-toe with a familiar face having played against and managed Orient boss Richie Wellens in the past.
But he reckons the O's - who needed penalties to see off Boreham Wood in the first round - will be in for a game despite the 31-place gap between them.
Mellon told the Latics' website: "I know Richie really well, I’ve managed him before. Our sons grew up playing together as well at Manchester United. I’ve known him for a long time.
"I’ve played against him myself which probably makes the two of us feel old. It’ll be nice to go down there but the two of us will want to win.
"It’s a great opportunity for us to see where we’re up to as a team. League One is a big step up, regardless of where Leyton Orient are in the league, it’s a big step up for us.
"We’ll give it everything we’ve got. We’re certainly going to attack it and try and win., that’s the type of team we are.
"We know it’s going to be really difficult, but we’ll make it really difficult for them as well because we’ve got some really talented players so we’re looking forward to it."