The Liberal party has sent one of its most senior figures to urge the former prime minister Malcolm Turnbull to either return to Australia to assist the Wentworth campaign or at least publicly endorse his replacement, Dave Sharma.

One of the party’s elder statesmen, the former federal MP Philip Ruddock, who is in New York to campaign for the Rohingya people, has asked to see Turnbull and will urge him to help.

Ruddock told Guardian Australia from New York that he had been in touch with Turnbull but did not yet have an arrangement, though as former colleagues they were likely to catch up.

“In my view obviously it would be better to have everyone in the tent than not, but that’s for Malcolm to consider. I think it would positive,” he said. “The decision will be his, not mine.”

Party officials are deeply worried about the prospects of holding Wentworth after the high-profile independent Kerryn Phelps entered the race on the weekend, as widely expected.

Phelps is well known in the electorate. A local GP and former deputy lord mayor of Sydney, who with her partner, Jackie Stricker, was at the forefront of the campaign for marriage equality, she has a high media and local profile.

Unlike the Liberal candidate, who hails from the north shore and has spent many years overseas as Australia’s ambassador to Israel, Phelps has lived and worked in the electorate for decades.

Even though Wentworth has never been won by anyone other than the Liberals, and Turnbull had built up a 17% margin, Liberal party strategists are deeply worried about just how much of that was a personal vote for the former PM.

They are warning a much more accurate measure of the strength of Liberal support is the 2004 result, when the then new member for Wentworth, Turnbull, won 41% of the primary vote against an independent, Peter King, who was ousted by Turnbull and then ran against him.

A public declaration of support for Sharma by Turnbull would be a strong signal to his personal support base not to punish the party for ousting him.

A ReachTel poll, commissioned by the Australia Institute and conducted on 27 August, that listed Sharma as the Liberal candidate (though he was yet to be preselected) showed the Liberal primary vote at 34.6%.

It also asked about two prominent independents, Phelps and Alex Greenwich, though Phelps had not yet declared and Greenwich is not running and is instead backing another independent, Licia Heath.

The ReachTel poll had 20.3% for Labor’s Tim Murray, 11.8% for Phelps, 11.2% for Greenwich, 8.9% Greens and 13.3% for all others.

If those numbers persist now that candidates are known, Sharma would likely lose, particularly if Phelps can overtake Murray, as his Labor preferences would flow to her ahead of the Liberals.

With a primary vote in the 30s or even the low 40s, Sharma would struggle to secure sufficient preferences. Phelps has now said she is not directing preferences but would need to be overtaken by Labor to deliver preferences to the Liberals.