The former England winger, who scored a stunning goal against Brazil in the Maracana, insists the Liverpool youngster should be allowed to develop at his own pace
Sterling is set to be deployed on the wing by manager Roy Hodgson for the Group D campaign against Italy, Uruguay and Costa Rica.
The 19-year-old Liverpool starlet has the hopes of a nation resting on his shoulders, after a brilliant Premier League campaign at Anfield.
But Barnes, who played at the 1986 and 1990 World Cups for England and scored a stunning solo goal against Brazil at the Maracana, insists that fans should not overburden the teenager.
"I still don't want to put so much pressure on him now that he has shown so much quality in the last few months of the season," Barnes said.
"Maybe he is going to be inconsistent because he is young. But in terms of what he did in the last few months of the season, he was probably the best player in England.
"Not the best English player; the best player in England, the best attacking player in England."
Sterling scored nine goals and provided seven assists for Liverpool in the Premier League in 2013-14.