Welbeck has only managed five goals in 30 appearances during a disappointing season for Arsenal.
The 27-year-old has netted 15 times in 36 caps for England, however, and Southgate has revealed that Welbeck is a direct replacement for Harry Kane, who is on the sidelines with an ankle problem.
"It's obvious to everyone that we have a very small number of players available for selection, on top of that, many of the top players are out," Southgate told reporters.
"With not long until the World Cup I now have to look beyond players in form for their clubs. Danny comes in as a replacement for Harry as a player who can run in behind."
Welbeck has scored three times in his last four appearances for England.