A stress fractue of the foot has seen Dyer out of first team contention at St James Park recently, and the youngster fears it will prove a fatal blow.
Shearer however feels that he has every chance to impress the Swede before the final cut.
"I hope and I'm sure that Kieron will be given every opportunity to prove himself and his fitness," said United's record signing, and former England captain.
"He is a big player and I believe he has a big future with England.
"If he plays the way we know he can and he gets his fitness back, then I've no reason to doubt he can make the World Cup."