Nmecha, who is on a season's loan at Deepdale from Manchester City, had been on stand-by for the Under-20s who are coached by former PNE manager Paul Simpson.
England face Germany at Colchester on Monday night (7pm) and Nmecha has joined-up with the squad for their preparations for the game.
While he has played from Under-16s through to Under-19s for England, he is yet to feature at Under-20s level.
Injury forced him to pull out of the England squad in September, while last month he was on stand-by.
Nmecha joined North End in August and has made 15 appearances - nine starts and six from the bench.
He is yet to open his scoring account in a Preston shirt.
Nmecha was born in Germany and lived there until he was nine but has chosen to play internationally for England.