Scharner has a great deal of empathy with Foster, who is on loan from Birmingham City until the end of the season.
"It's very difficult for me to say but I think it is very difficult to play for England from what I see from outside," said Scharner.
"I think that's why he wants to concentrate on his performance for his club and not get away from it when he plays for England as well.
"I think he also picked up an injury that he couldn't get rid of because he was in the England squad.
"So, from my point of view, it was a good decision to get fit first.
"I think it is a burden. The expectation is very high."