Though they were among those not included in the 31-man Ireland World Cup squad named on Monday, scrum-half Kieran Marmion, utility back Will Addison and back row Jordi Murphy remain involved with training at Carton House.
Joe Schmidt wants the trio primed should Ireland suffer any serious injuries during this weekend's final warm-up game against Wales.
Players discovered they had not been selected via phone calls from the head coach.
"[Their reaction was] unbelievable," said Schmidt at a press conference on Tuesday.
"I spoke to them on the phone. I said, 'Look, this is not the phone call you want to get, this is not the conversation I want to have. You've fallen outside the squad and there's a very narrow margin in that'.
"I discussed a few game-related things with them. Those three guys, as young men, they would be brilliant in the squad.
"It's very easy for someone on the sidelines to throw barbs about who has been left out but you can only find 31 spots.
"Those three guys were unbelievably good and I said, 'Would you come in and train with us Monday, Tuesday and maybe further on through the week?' They said, 'Yep, no problem, I'll be there'.
"They've trained really well, which gives us confidence because we could lose somebody on Saturday or someone during the tournament."
Regarding the selection of Luke McGrath as backup to Conor Murray ahead of Marmion, Schmidt said:
A thin wire separated them. The strength of Luke's kicking game was just the balance that we felt we need to take the pressure of the kicking games from our 10's; we can mix it up between our halves and further out.
They're both incredible tenacious. They're smart and sharp around the fringes. Both are incredibly courageous defenders. It was very much a dead heat in so many areas. Luke's kicking game narrowly tipped it in his favour.
Schmidt also further elaborated on Devin Toner's omission saying that due to injury, the giant second row had been behind others throughout the pre-season.
"For Dev, he was behind the eight-ball," said Schmidt.
"He had that ankle injury. So, physically, he was playing a little bit of catch-up. It just meant that other guys got a little bit of a headstart on him.
"It was a very narrow decision, a very tough call. I've known him well for 10 years and have a huge amount of time for him, not just as a player but as a person. He's real quality. You never make those decisions lightly."
Photo by Brendan Moran/Sportsfile
