"Andy's out of the games against Macedonia and Croatia with a hamstring injury," England head coach Steve McClaren told the FA's official website.
"It's a real blow because he's made a massive impact already with Everton this season and I've been hugely impressed by him. He's got such a great attitude and is a constant threat to any defence.
"He was certainly knocking very hard on the door for a place in the team, so it's a disappointment to lose him.
"However, I've spoken to Peter Taylor and I can confirm that Darren Bent will now join the senior squad when we meet on Tuesday.
"We're fortunate that we're able to call Darren up from the Under-21's. He's already got experience of been involved in several senior squads and he's a player with excellent ability and a real goal threat."