Rafael Benitez and Gary Cahill have raised concerns about the balls being used for the goalline technology trial in Chelsea's Club World Cup semi-final.
The European champions' tournament opener against Monterrey in Yokohama on Thursday will witness the competitive debut of the GoalRef system, in which a microchip inside the match ball determines whether it has crossed the line.
But the technology has made the balls heavier, according to Chelsea's players. Interim manager Benitez said: "It's too hard when you kick the ball. The players the first day, they thought it was too hard."
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