Northampton or Rotherham.
FA CUP DRAW
Northampton boss Colin Calderwood:
"What an attractive fixture for the winners of the replay," he told Sky Sports News.
"I'm sure this will add a few to the gate at Millmoor. But it's important to remember this is an extremely tough ask for us to go to Rotherham and win. We’ve got a big game coming up in the league against Torquay - but what a great incentive this is.It will keep everyone eager. The league games are all important to us, but this is the cherry on the icing on the cake."
The last time the Cobblers faced United was also in the FA Cup in 1970 - when six goals from George Best for United helped secure an 8-2 win.
United went to Rotherham for a League Cup second-round tie during the early days of Fergies reign when Peter Davenport's winner set United up for an aggregate 6-0 triumph.