D'Arcy, who travelled to New Zealand with the 2005 Lions before being called up as a late replacement on the recent tour of South Africa, limped off during the first half of Ireland's comfortable win over Wales at the weekend.
He suffered deep bruising above his left knee and is currently being closely monitored by the Irish medical team.
D'Arcy will miss today's light session and will continue to be assessed throughout the week.
Double tryscorer and fellow Lion Keith Earls is a slight worry after complaining of tight calves but the Munsterman is expected to be available for the Croke Park clash.
Lions team-mate David Wallace, who toured with Britain and Ireland's elite nine years ago and was also a Test starter in 2009, is in a similar situation having received an accidental scratch to the eye during the 27-12 triumph over Wales.
Like Earls, he will be monitored during the week but is likely to be fit when Ireland go in search of another Triple Crown success against a winless Scotland.