Ireland edged battling Samoa 17-13 in a World Cup warm-up match in rainy Bayonne on Saturday but suffered a major setback ahead of the global showpiece when veteran prop Cian Healy limped off with what appeared to be a calf injury.
Healy, playing in his 125th international, was hurt in the first half and was in serious pain as he was helped to the touchline.
With coach Andy Farrell set to reveal his squad for the World Cup on Sunday, the 35-year-old Healy faces a worrying race for fitness.
"I saw what you saw. He pulled up sharp and struggled to get off the field. We'll try and get that assessed as soon as we possibly can," Farrell told broadcaster RTE.
On the match itself, Farrell added: "It doesn't all go your own way, sometimes you've got to find a way and you know what we played against a very good side today.
"Samoa are a good side across the board, obviously very well coached and good players and we found a way, three tries to one. It's pleasing to come away with a victory."
Ireland showed 12 changes from the side that thrashed England 29-10 last weekend.
They were ahead after just nine minutes on Saturday when full-back Jimmy O'Brien scored a try, set-up by a smart crossfield kick from fly-half Jack Crowley and support work from winger Mack Hansen.
Crowley, who added the conversion for 7-0, was playing in place of suspended first-choice fly-half and captain Johnny Sexton.
Healy's evening ended after 20 minutes and Samoa began to get a foothold in the game.
Full-back Duncan Paia'aua scored Samoa's only try in the 36th minute, racing away after an attempted pass from Irish centre Stuart McCloskey had hit him in the face.
Former New Zealand fly-half Lima Sopoaga succeeded with the conversion for 7-7.
Sopoaga made his last All Blacks appearance in 2017 but benefits from a World Rugby rule change to play for the Pacific Islanders through family links.
Sopoaga then kicked a penalty in the closing moments of the first half for a 10-7 interval lead for the Pacific islanders.
The 32-year-old was successful with another penalty five minutes into the second period as Samoa edged to a 13-7 lead.
Ireland cut the deficit to 13-12 moments later when scrum-half Conor Murray scored off a clever chip ahead from Jacob Stockdale but Crowley missed the conversion.
Irish forward power allowed them to take charge as replacement hooker Rob Herring crashed over off a maul with just over an hour played.
Crowley again went wide with his kick but a 13th successive win for the Irish was secured.
Ireland begin their World Cup campaign against Romania on September 9 with Samoa facing Chile in their opener on September 16.