"I didn't think the gaffer was being serious when he called to tell me this morning," Lallana told Southampton's official website.
"I was at home about to head into the training ground when he called - I must have asked if he was having me on a dozen times!
"I'm totally shocked to be honest."
"It's such a proud accomplishment to be called up to play for your country at any level, but to be called into the senior side is probably the proudest moment of my career so far," added.
"It is every player's dream to represent your country at the top level.
"I'm realistic in accepting I might not be that heavily involved, but the fact that I will be around such experienced international players is something I am really excited about."