Holders Rangers did manage to play over the weekend, but they played out a 3-3 draw at Hamilton. They now know victory in the replay will see them travel to SPL rivals St Mirren.
If Celtic manage to overcome Morton in their rearranged clash, they will travel to Dunfermline.
Of the two remaining non-league sides, Edinburgh City have been handed a trip against capital rivals Hibernian - but they must first get past Montrose.
Inverurie Loco Works are also still in the draw, but they have still to play Ross County. If they win that they will be at home to Albion Rovers or Stirling.
Draw in full:
Dunfermline v Morton or Celtic, Forfar or St Johnstone v Dundee United, Hibernian v Edinburgh City or Montrose, Livingston or Dundee v Ayr United or Brechin City, Raith Rovers or Airdrie United v Aberdeen, Kilmarnock or Falkirk v Inverness CT or Motherwell, St Mirren v Hamilton or Rangers, Ross County or Inverurie Loco Works v Albion Rovers or Stirling.
Ties to be played weekend of February 6 & 7.