Shot clock will be introduced as part of Grand Slam shake-up
Top tennis stars will come under a 25-second shot clock in Grand Slam tournaments starting at the Australian Open in January.
The shot clock is just one of a number of changes ratified by the sport's Grand Slam Board during two days of meetings in London this week.
Its immediate introduction will catch some by surprise after it was trialled at both US Open qualifying and the recent Next Gen Finals in Milan.
World No.1 Rafael Nadal is an opponent of the move, insisting in August it would ruin the chances of future epic matches.
Nadal said: "I think (the shot clock) is not possible for a great show. But if you don't want a great show, of course it's a great improvement."
Another change involves the introduction of a potential fine for a player who either withdraws late or performs below what are deemed by the GSB to be "professional standards".
Now, any player who plays in a first round match and retires, or does not perform sufficiently well, could potentially forfeit his whole first round prize money as a result.
Meanwhile, the GSB also confirmed that all the Grand Slam tournaments will revert from 32 to 16 men's and women's seeds from the 2019 competitions onwards.