Promising MPs Josh Frydenberg and Steve Ciobo, who serve as parliamentary secretaries to Prime Minister Tony Abbott and Treasurer Joe Hockey, have emerged as the frontrunners to take the vacant post.

If one or other of that pair was promoted, three Liberal MPs - Dan Tehan, Kelly O'Dwyer or Christian Porter - have been tipped to fill the vacancy created.

Senator Sinodinos stepped back from his portfolio almost two weeks ago over his links to Australian Water Holdings, a company linked to former Labor powerbroker Eddie Obeid.

He has denied any wrongdoing over allegations that he stood to make up to $20 million from his role as a director at the company and says he will be vindicated at the ICAC hearing, where he is scheduled to appear on Wednesday.

Mr Abbott strongly endorsed Senator Sinodinos when he stood aside, arguing he had done the ''right and honourable thing'' in stepping aside before the Coalition's first federal budget.

''He is a fundamentally decent man. I am confident that he will be able to return to his duties, his ministerial duties soon but in the meantime he has done the right and the honourable thing,'' Mr Abbott said.

But Liberal MPs said there was a developing view in the party room that Senator Sinodinos will be sidelined for longer than expected by the wide-ranging ICAC inquiry, and suggested it could be difficult for him to resume his current portfolio once the hearing concludes.

If Mr Abbott is forced to replace Senator Sinodinos on the frontbench, his choice of successor could be seen as a vote of confidence, by proxy, in either Mr Hockey or Immigration Minister Scott Morrison.

Mr Frydenberg played a key role behind the scenes in the government's red tape-focused repeal day and is an ally of Mr Morrison and Environment Minister Greg Hunt.

Mr Ciobo already reports to the Treasurer and is seen as part of the ''Hockey Club'', a group of economically dry MPs which includes rising stars, Finance Minister Mathias Cormann and junior Infrastructure Minister Jamie Briggs.

Coalition MPs confirmed Mr Ciobo would be Mr Hockey's choice for assistant treasurer if Senator Sinodinos does not return.

''If Tony wants tensions between Joe and Scott, he'll promote Josh,'' one MP said, ''it just depends on what the PM wants to do.'' A second MP said that no one had written off Senator Sinodinos' chances of returning but admitted there was ''a lot of chatter'' about the vacancy and ''Arthur could be gone for a while''.