The former Newcastle United goalkeeper was not included in Roy Hodgson's England squad for upcoming friendlies with Republic of Ireland and Brazil, and although Lennon says his Three Lions chances are not in immediate danger, he does fear Forster may be lured to the Premier League if a club happened to show interest.
"In terms of his England prospects, I'm not convinced it has done any serious damage to him. But I am worried that people may feel he has to go and play at a higher level to maintain his spot in the England squad," he said.
"It is a concern for me - that is the reality. He has been outstanding for us and has shown the calibre of keeper he is. They know what he is like and know what he can do.
"Maybe they feel he has to play at a higher level on a more consistent basis. We have to try to give him that with Champions League qualification next season."