Storm assistant Adam O'Brien has backed Brodie Croft to retain the No.7 jersey ahead of Jahrome Hughes in the AAMI Park grand final qualifier - unless coach Craig Bellamy changes his mind again.

Bellamy has used a horses for courses approach for his halfbacks this year to tackle life without Cooper Cronk but appeared to find a keeper in Croft.

The youngster came back from a knee injury to help spark the Storm's 29-28 qualifying final victory over South Sydney, appearing to jump the No.7 queue ahead of Hughes and Ryley Jacks.

But O'Brien has kept Cronulla guessing, providing no guarantees for Croft despite the youngster being named at halfback for the knockout final.

"If Brodie is the best choice then that's the way we'll go but if it's Jahrome then it will be Jahrome," he told Fox Sports' NRL 360.

Croft will back himself to keep the No.7 jumper despite being dropped twice earlier this year.

He has played three of Melbourne's last four games and stepped up on finals debut to have two try assists and two line breaks, running 77m against the Rabbitohs in their qualifying final.

Overall Croft has played 10 games at halfback, Jacks nine and Hughes five with regular fullback Scott Drinkwater even getting a game recently.

Bellamy's left field approach ensures Melbourne must become the first team to win a premiership without a settled halfback in three decades if they are to defend their NRL title this year.

"I can understand why people would not be warming to the idea," O'Brien said.

"But the advantage we have is that the players themselves - Jahrome and Brodie - are comfortable with the situation.

"And just as important the guys who play outside them - our back-rowers and centres - are also comfortable with it.

"It's what is best for the team that week and thankfully both of those young boys are on board with that."

If he plays, all eyes will be on Croft as the Storm strive to give retiring fullback Billy Slater a fairytale finish in next week's grand final.

O'Brien agreed with Bellamy's comment that 35-year-old Slater may be retiring a year too early.

"I can understand why Craig made those comments because his output has never dipped," he said.

"If anything it has only increased."

Australian Associated Press