It is hoped the pair will feature in the latter stages of the five-match programme designed to leave the squad battle-hardened for the tournament in New Zealand.
But team manager Paul McNaughton has admitted that D'Arcy and Ferris, who are key performers, remain doubts as they continue their rehabilitation from respective ankle and knee problems.
Taking unfit players to a World Cup is risky, but McNaughton has refused to rule out the possibility.
"Gordon and Stephen face a race against time but are making progress," he said.
"If there are two guys who may not play before the World Cup, then it's those two.
"We're hopeful that they may be ready for game time, maybe in match three or four of the summer series. They are unlikely to play in the first two games.
"It's a preference that they have some game time before they go, but we'll never say never on anybody.
"A player could be just a week away from full fitness but it would be dangerous to play him in a game.
"We always have that option. It's our preference that everyone will get some game time."
Ireland are likely to field a trio of long-term absentees when they open their warm-up campaign against Scotland at Murrayfield on Saturday.
Hooker Jerry Flannery and full-backs Rob Kearney and Geordan Murphy are now available for selection and desperately need game time.
"Flannery (calf), Kearney (knee) and Murphy (ankle) are ready to go. They were involved in contact last week," said McNaughton.
"Flannery has been out for quite a while now (since January).
"He has been getting specialist rehab on a one-to-one basis during the summer, but over the last two weeks has kept up fully in training.
"We're pleased to see him take part in everything from contact to scrummaging.
"In general the injury situation has been getting better over the last couple of weeks, but we have five matches and need to give guys game time.
"We're hopeful that every player will partake in some games."
Ireland name their team to face Scotland at Thursday lunchtime.
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