20 year old McDermott has played for Fulham's reserves for the past three seasons since signing for the London club from Newcastle United.
He's played for the England Under 18's and subject to league approval should join up with the rest of the Swindon squad on Thursday on loan until the end of December.
The other loan players already at the club are Partick Collins from Sheffield Wednesday, Andy Gurney from Swansea City, Tom Heaton, and Colin Heath both from Manchester United.