Simon Zebo limped out of Ireland's training session in Galway on Tuesday morning with a suspected knee injury.
The Munster winger, 25, appeared to be in pain as he hobbled off the pitch and the Irish medical staff then placed an ice pack on his knee.
Gordon D'Arcy and Isaac Boss were also unable to complete the session because of knocks.
Boss appeared to be troubled by a hamstring twinge while the nature of D'Arcy's injury was unclear.
All three players have been named in Ireland's initial 45-man training squad for the Rugby World Cup, which they will begin against Canada in Cardiff on 19 September.
Zebo started Ireland's opening four Six Nations matches this year although he was replaced by Luke Fitzgerald as they beat Scotland in their concluding game to clinch the title.
Centre D'Arcy, 35, has won 81 Ireland caps but did not feature in this year's Six Nations Championship and has said that he will be retiring after the World Cup.
Ireland's final 31-man World Cup squad will be named after a series of four warm-up matches.
They take on Wales in Cardiff on 8 August before hosting Scotland a week later at the Aviva Stadium.
On 29 August, Wales come to the Aviva Stadium, with the final warm-up game taking place against England at Twickenham on 5 September.