Old Trafford coaches asked to have a look at him after he played for Reading Under-17s against United at the start of the season and although Reading went down 6-1, Campbell is said to have capped an excellent display with a stunning goal.
Campbell travelled to Carrington on Sunday for a seven-day trial after impressing in an under-17 match early in the seaason.
Reading chief Alan Pardew said: "I want to get a good relationship with that club with the staff they have and this is a good link to have between the two of us. It is also great experience for Darren."