Walters was a second-half substitute during Ireland's 2-1 defeat to France on Sunday, despite admitting he was not fully fit.
Walters, who missed Ireland's two previous games, has been suffering from an Achilles injury for much of the summer, but was still thrown on midway through the second half of his team's defeat in Lyon.
The Stoke City star had a couple of half-chances to salvage a leveller for Martin O'Neill's men, who saw Robbie Brady's early spot kick cancelled out by Antoine Griezmann's second-half brace, but he was powerless to prevent a brave exit.
Ireland's misery was compounded moments after Walters' arrival 25 minutes from time, as Shane Duffy was shown a straight red card for a professional foul on Griezmann.
After failing to make an impact from the bench, Walters was quizzed about whether he was truly fit enough to play,
According to the Stoke Sentinel, he replied: "Probably not. I had a little tear in it and we worked morning, noon and night to get out there and it's disappointing I haven't been able to play many games."
Reports suggest Walters will now be given an extended break by Stoke boss Mark Hughes before linking up with his Potters teammates, who are gearing up for a preseason trip to the United States for a friendly against Orlando City on July 27.