Officials were on Tuesday night preparing to make two changes to their Ashes squad, with Parramatta winger Josh Addo-Carr expected to be called up.
Newcastle centre Bradman Best would also loom as a likely option, after being seriously considered for the initial squad before being pipped by Brisbane's Gehamat Shibasaki.
Best was instead named in the Prime Minster's XIII squad to take on Papua New Guinea, in a clear sign he is in selectors' sights as a future Kangaroo.
The loss of Parramatta's Lomax to a hip strain and Melbourne's Coates with an achilles tendon is is a brutal setback for coach Kevin Walters, given they had strong chances to be the two starting wingers.
Coates was spotted leaving Accor Stadium with a moon boot on his left foot on Sunday night, after the Storm's grand-final loss to Brisbane, and has a minor achilles tear. He is expected to be fit in time for Melbourne's pre-season.
Lomax, meanwhile, finished the season for Parramatta but has since succumbed to a hip injury.
Australia's squad already features Mark Nawaqanitawase, who came to life on the Sydney Roosters' wing in the second half of the season.
Brisbane pair Shibasaki and Kotoni Staggs are the two other centres named, while Penrith fullback Dylan Edwards has previously played on the wing for Australia in 2023.
Lomax's selection in the squad had come with the Eels winger linked to a move to breakaway rugby competition R360.
He is under contract to the Eels until the end of 2028, and his management have insisted he will not walk out on that deal.
Parramatta coach Jason Ryles has suggested, however, he would have a serious think about releasing Lomax if requested.
Kangaroos coach Kevin Walters had said at Monday's squad announcement that he had spoken to Lomax and was confident he was in the right frame of mind to play for Australia.
"Having spoken to Zac himself, he certainly has a good mindset around the tour," Walters said on Monday, prior to the injury news.
"I have had several conversations with him, he is right to go."
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