Tozer, 20, is expected to start for the Cobblers at Anfield after completing a month-long loan move from St James' Park as Dean Beckwith is struggling with a thigh strain.
Northampton manager Ian Sampson, whose basement side clinched a dream tie at Anfield with a 4-2 penalty shootout win at Championship side Reading after sharing six goals over 120 minutes, has been given a timely lift by the arrival of Tozer, who is highly rated at Newcastle.
Sampson said: "He's a player with an excellent pedigree and someone who will do us a good turn over the next few weeks.
"He was really keen to come and already his attitude to get stuck in and do well for this club has impressed me. I tried to bring him in last season, but it didn't quite work out."
Sampson's young side, who beat Brighton 2-0 in the first round, are determined to enjoy themselves against Roy Hodgson's superstars.
Goalkeeper Chris Dunn, 22, said: "It's a great one to play. It's going to be a great experience for the lads, obviously we're a young side, but we go there with no fears. We've nothing to lose. All the boys are looking forward to it.
"We don't get to play at these places week in, week out so when you do get the chance you've got to make the most of it. We've got to enjoy the occasion.
"It's going to be quicker and there's going to be periods of the game where we're going to have to keep our shape and discipline when we don't have the ball.
"But it's going to be a good learning curve for the young lads and if we can just keep our concentration we give ourselves a chance."