The England U-21 star did not take part of the team's training during the last couple of days, and manager Steve Coppell revealed that Lita is in trouble.
"Leroy is in a great deal of pain, he woke up and stretched while in bed and he has done something to his leg!" Coppell was quoted by BBC Sports on Wednesday.
The Royals will kick-off their Premiership new season with a tricky fixture, facing champions Manchester United at Old Trafford on Saturday, but Lita's injury will definitely rule him out.
"It's a point of laughter but a serious business for him because he's going to be out for three or four weeks."
"It is not an injury that should be ridiculed or made light of. It looks to be a problem with a nerve. Maybe he has displaced one, but he could hardly walk on Monday and had to sit out training."
Lita scored seven Premiership goals for Reading last season as Coppell's team finished eighth.