Liverpool forward Leanne Kiernan and Birmingham City's Jamie Finn are other notable omissions.

The Republic will play their first ever World Cup finals match against co-hosts Australia on 20 July.

After naming a 32-strong training group, manager Vera Pauw has cut her squad down to a final 23, while three travelling reserves will also be named.

Despite only making her Irish debut this year after switching allegiance from England, it had been hoped that United defender Mannion would be passed fit following a series of assured performances in the green jersey.

Finn omission the 'toughest' decision

However, Pauw said both Mannion and Campbell's chances of inclusion were "no go" as a result of their injuries, which means that the Irish will be without the Liverpool player's long-throw capability in Australia.

"There was not even a small chance that they would be ready for a World Cup," said an emotional Pauw after she announced her squad.

The Republic boss said Finn's omission had been the "toughest" after having been involved in every World Cup qualifier and that "the data" showed Liverpool forward Kiernan hadn't fully recovered from her recent injury problems after a season where she had limited minutes for her club.

"That [Finn's omission] has really broken our hearts because she was in all the qualifying campaign.

"But as we have all seen, we have changed two target players with Kyra Carusa up front and brought Heather Payne to the right into her [Finn's] position)."

The squad will face Australia, Canada and Nigeria at this summer's World Cup

Finn will travel to Australia along Birmingham team-mate Harriet Scott and Lewes goalkeeper Sophie Whitehouse as training players with injury-enforced changes to the 23 permitted before Fifa's deadline on 10 July.

"We wanted to give Leanne the chance to grow in two week to get ready and she showed very good moments in the game against Zambia but the data showed that the explosive actions that she made, the time between them became longer," added the Dutchwoman.

"This was a hard day for all of us. And also for the players who made it. They feel more the pain for the players who didn't make it rather than celebration for themselves. But we are fully, fully behind the choices that we had to make."

Scott is one of the big losers amid a competitive defensive selection.

Celtic defender Claire O'Riordan earns a place in the Republic of Ireland's World Cup squad after an impressive display in the friendly win over Zambia last week

Celtic defender Claire O'Riordan and Hearts midfielder Ciara Grant were the biggest beneficiaries of Pauw's deliberations after the pair played a key role in last week's friendly win over Zambia.

West Ham's Izzy Atkinson wasn't included in Pauw's initial training squad but was drafted in for the Zambia game due to Campbell's fitness issues.

The 21-year-old started the friendly in Tallaght and adds to the Republic's left-sided options for the tournament.

Highly-rated Shamrock Rovers teenager Abbie Larkin has been included after impressing at the Tallaght club, while US-born Sinead Farrelly continues her remarkable story with selection.

After retiring aged 25 in 2016, Farrelly played a key role in exposing the NWSL abuse allegations before returning to the pitch earlier this year. She made her Irish debut, her only cap to date, against her native USA in April and is now heading to the World Cup.

Following the opener against Australia in Sydney, Pauw's side face Olympic champions Canada in Perth and Nigeria in Brisbane as they look to progress from Group B.

Republic of Ireland squad

Goalkeepers: Courtney Brosnan (Everton), Grace Moloney (Reading), Megan Walsh (Brighton & Hove Albion)

Defenders: Heather Payne (Florida State), Louise Quinn (Birmingham City), Niamh Fahey (Liverpool), Aine O'Gorman (Shamrock Rovers), Chloe Mustaki (Bristol City), Claire O'Riordan (Celtic), Diane Caldwell (Reading), Izzy Atkinson (West Ham), Megan Connolly (Brighton & Hove Albion)

Midfielders: Katie McCabe (Arsenal), Denise O'Sullivan (North Carolina Courage), Lily Agg (London City Lionesses), Ciara Grant (Hearts), Lucy Quinn (Birmingham City), Sinead Farrelly (Gotham City NYC), Ruesha Littlejohn (Aston Villa)

Forwards: Amber Barrett (Standard Liege), Kyra Carusa (London City Lionesses), Abbie Larkin (Shamrock Rovers), Marissa Sheva (Washington Spirit).

Training players: Sophie Whitehouse (Lewes), Harriet Scott (Birmingham City), Jamie Finn (Birmingham City)