The 25-year old goalkeeper was overlooked by Three Lions boss Roy Hodgson for upcoming friendlies with Republic of Ireland and Brazil with some critics suggesting he would need to continue his career in England in order to depose either Joe Hart, Ben Foster or Alex McCarthy in the national team plans.
“It’s a tough one for me with England,” said Forster.
“Celtic’s been fantastic for me. This season couldn’t have gone much better, both personally and as a team.
“It’s disappointing not to be in this England squad but I’ve got to be looking towards the World Cup and trying to be on the plane.
“So I’ll just have to do whatever is necessary to make that squad.
“I’ve got quite a while left on my contract here and if we can get through the Champions League qualifiers, which will be tough, to get in the group stage again would be something special.
“We’ll just have to wait and see.
“I didn’t get an explanation as to why I was left out this time, although I haven’t spoken to anyone at England.
“We haven’t got that long off in the summer anyway so you just have to take the positives from it.
“I’ll get a good rest and come back raring to go. My plan is to get some sunshine and relax. It’s been a very long season.”