Christopher Markus & Stephen McFeely wrote the script for the film, which is being directed by Joe Johnston. It wasn't quite clear what the extent of Whedon's potential script polish could be, but it was also said that Whedon was polishing Zak Penn's script for The Avengers as well.
We'll be sure to keep you posted on any new developments on Captain America: The First Avenger as soon as we have more information.
Captain America: The First Avenger was released July 22nd, 2011 and stars Chris Evans, Hayley Atwell, Sebastian Stan, Tommy Lee Jones, Hugo Weaving, Dominic Cooper, Richard Armitage, Stanley Tucci. The film is directed by Joe Johnston.
Marvel's The Avengers was released May 4th, 2012 and stars Robert Downey Jr., Chris Evans, Mark Ruffalo, Chris Hemsworth, Scarlett Johansson, Jeremy Renner, Tom Hiddleston, Clark Gregg. The film is directed by Joss Whedon.