The vuvuzelas created a racket at last year's Confederations Cup
Former England captain Bryan Robson believes World Cup managers could struggle against the noise of the South African plastic trumpet, the vuvuzela.
Robson, who is manager of Thailand, saw his side lose 4-0 to South Africa in a warm-up match in Nelspruit on Sunday.
But the deafening and tuneless noise from the trumpet drowned out his instructions from the bench and he had to call players over to the sidelines.
"With that noise they could have an advantage in the World Cup," he said.
"If the atmosphere is like that in the World Cup it will raise the level of the players a little bit. If the supporters are behind them like that, it will be a big boost.
"The coaches at the World Cup are definitely going to have to inform their players beforehand that they will have to communicate effectively with each other on the field.
"It's very difficult to get any message to the players from the bench. Coaches are going to have to make that known to their players."
Complaints about the vuvuzela during last year's Confederations Cup in South Africa were rejected by Fifa, who said there would be no ban on the long plastic instrument at the World Cup.
But South Africa coach Carlos Alberto Parreira is happy for the vuvuzela to continue when the tournament starts next month.
"We have to reinforce that advantage," he said. "We want it louder and louder."