The two-time European Champions are having a look at Reading's young star following an impressive showing, and a fantastic goal, during the under 17s 6-1 defeat to United.
Whilst it is possible that the deal could become permanent, 16-year-old Campbell is expected to return to Reading in time for the under 17 Academy League clash with West Ham.
Royals boss Alan Pardew revealed that he sent his youngster up North to Old Trafford for a week in an attempt to forge good links with Sir Alex Ferguson.
Pards told readingfc.co.uk: "This is purely to get a connection with United. We've got Matthew Upson on loan from Arsenal so we've got a connection with them, it's good to have clubs interested in us.
"Darren played against United at the start of the season for the Under-17s and he did very well. Darren is one of our top boys, and I've got no problem with it."
Campbell has appeared in the reserves twice and has been capped at youth level by both England and Scotland.