Young Brisbane Broncos star Selwyn Cobbo has already shown plenty of growth during the club's first few weeks of pre-season training, and while the talented outside back has bulked up during the off-season he's lost none of his searing pace.

Cobbo confirmed his status as one of the fastest men in the NRL as the club did 40-metre sprint tests this week – with the talented 20-year-old finishing second among the club's ranks, only behind Deine Mariner.

Cobbo clocked a time of 4.7 seconds for the challenge, with Mariner beating him by the narrowest of margins with 4.6 seconds. There is a telling point of difference, however – Cobbo is currently registering at 108kgs during training – almost 20 kilos heavier than Mariner.

While Cobbo is expected to return to a number closer to his usual playing weight as the season approaches, it's a positive sign for his physiological development ahead of what he's hoping will be an even bigger season than 2022 after just his second full pre-season in the NRL.

Both Cobbo and Mariner were faster than new recruit Reece Walsh.

“I wouldn't be surprised if 2023 ends up being a bigger year than 2022 for Selwyn,” Cobbo's agent Tas Bartlett told the Daily Telegraph.

“I think Selwyn can physically get bigger than Latrell (Mitchell).

“Selwyn did some testing at the Broncos the other day and the only guy faster than him is Deine Mariner.

“It's pretty frightening how fast Selwyn can move for a big man.

“He's returned to pre-season a couple of kilos overweight, but for someone as athletic as Selywn, it won't take him long to get back to his optimum weight.

“Selwyn played at 100kgs last year and the Broncos want him up to 102kg this year. He's a year older, his frame will naturally fill out with weights which is pretty scary for NRL opponents.

Despite the missed opportunity, Cobbo's omission from Mal Meninga's World Cup team is seen as a blessing after he admitted he was struggling with the demands of a first full NRL season towards the end of the 2022 campaign.

“People forget how young and raw Selwyn is. He was a blank canvas coming into the Broncos and is learning what it takes to be a professional in the NRL.

“Not going on the World Cup tour was a good thing for Selwyn. He can have three months at the Broncos to do the heavy lifting and the work to get his body and mind right for his second full season.”