An outside back, Sio has scored 13 tries in 14 games for a struggling Eels team this season.
Rovers are believed to have added two players from Australia to their squad for next season, and it would seem that Sio, 23, is one of them.
“Ken is a very good player,” Chester told the Hull Daily Mail.
“We have been talking to quite a few players in the NRL.
“Ken is one of them and hopefully we’ll have some news in the not too distant future on certain individuals.
“It was a successful trip to Australia.
“We had a long list of players and we narrowed that down to four or five.
“We are looking for outside backs because we are lacking speed on the outside edge.
“If we can get a couple of outside backs then I’ll be happy.”
Chester insisted that he expects the player to go to Australia at some stage, but does not know whether or not it will be next season.
“Josh hasn’t said anything to me about his future yet,” the coach explained.
“If he goes, he will be a massive loss, but until I get the phone call from the chairman we’ll regard Josh as a Hull KR player.
“There is a lot of speculation and Josh has an ambition to play in the NRL.
“Whether that’s next season or not, I don’t know.”
Chester also confirmed that nothing has been decided yet about his own long-term future at the club, with him in charge of the Robins until the end of the season.