The NSWRL has moved to reduce the impact of the forecasted heatwave by moving some of its matches to start as early as 7.45am, while Canterbury and Penrith's twilight NRL trial at Belmore has been delayed an hour to avoid the hottest part of the day.

It comes as the A-League announced Saturday's twilight match between Newcastle and Melbourne Victory at Hunter Stadium has been postponed to Monday night and NSW premier cricket discuss contingency plans for grade and junior matches as a result of the predicted sizzling temperatures across the state.

The NSWRL has tried to avoid matches being played between 11am and 3pm on Saturday, having to reshuffle its Harold Matthews, SG Ball and women's competition for the safety of the players.

Club doctors will be given the final say as to whether play will go ahead, and will cancel matches if they deem it unsafe.

There are only two NRL trials in Sydney this weekend, with South Sydney hosting Manly at Campbelltown on Saturday night as well as the Bulldogs-Panthers match at Belmore.

NRL chief medical officer, Dr Paul Bloomfield, has reiterated the importance of all clubs following the code's heat guidelines. He is hopeful clubs will implement extra measures to protect players given it is still only the pre-season.

"We would expect our current heat guidelines to be followed in all trial matches. In fact we would anticipate that clubs would be more conservative based on the fact that these are trial matches," Bloomfield said.

"There are already other procedures in place for trials which would limit the impact of heat, including larger squads and unlimited interchange.

"That said, all club doctors are well aware of those guidelines and will be making decisions in the best interests of the players."

There will also be a drinks break mid-way through each half, as well as an extended half-time break to allow players time to recover.

Doctors will determine whether matches should go on by adhering to NRL guidelines, which takes into consideration the temperature, the age of the athletes, the regularity of fluid intake, the duration of the match and the time of day it is played.

Meanwhile, Sydney's grade cricket competition and junior games across the city could be called off this weekend amid the scorching heat engulfing Sydney.

NSW Premier Cricket have spent the week consulting stakeholders and are holding a teleconference on Thursday night to develop a contingency plan for managing the heatwave.

Measures taken to manage player welfare in junior cricket will be left up to individual associations, all of which have been encouraged to err on the side of caution.

"There's a range of options available to us, and one of those options is to abandon play in all matches," Premier Cricket manager Roy Formica said.

"There's a range of other options that might include amendments to the playing conditions like reduced hours, starting earlier, having longer breaks.

"Even though we've consulted sports doctors and other medical professionals, there's not magic formula for that sort of stuff, there's a heat index that we look at as well but no magic formula unfortunately and every state's different."