Tatum has been approached to play the title role, that of a weak World War II solider who is injected with a serum and transformed into a musclebound superhero. The Dear John star joins Ryan Phillippe, Chris Evans, Mike Vogel and Garrett Hedlund as candidates for the superhero role in Joe Johnston's action-adventure film.
Knightley, meanwhile, is under consideration for the female lead Peggy. Brit actresses Alice Eve and Emily Blunt are also on the shortlist for the part. The Matrix star Hugo Weaving is in negotiations to portray villain Red Skull.
The First Avenger: Captain America will shoot in the UK this summer and is slated for release in July 2011.