The 20-year-old scored five goals during his spell at Vicarage Road as well as being one of the main suppliers of assists to strike duo Marlon King and Darius Henderson.
But despite his sparkling form for the Hornets boss Southgate does not want to put too much pressure on the latest recruit from the Boro production line.
He told the club's official website: "I'm not bringing him back thinking he's going to start turning our season around for us, he's a young player and I don't want to put any pressure on him.
"We've always known Adam's talent and being away from home will have done him a lot of good. Playing in a physical league was important too, as well as learning the other sides of the game."