Bettinelli joins fellow goalkeepers Jordan Pickford, Jack Butland and Alex McCarthy in the squad, having reported to St George's Park on Tuesday evening.
Pickford did not take part in training on Tuesday, leading Southgate to bring in further back-up as the 'Three Lions' prepare to get their UEFA Nations League campaign underway.
The call-up caps off a remarkable 12 months or so for the goalkeeper, who started last season on the bench for the 'Cottagers' in the Championship.
However, he quickly forced his way back into the team and has successfully seen off competition from new arrivals Sergio Rico and Fabri to reclaim his starting place this season.
The news came just hours after it emerged that Liverpool playmaker Adan Lallana had been forced to withdraw from the squad due to a groin problem.
September 4, 2018