In February 2015, Barnes performed a high tackle on Chelsea's Nemanja Matić, who was sent off for pushing him in retaliation. Barnes did not receive a booking for the challenge, and The FA confirmed that they would not take retrospective action as that was not normal procedure for attempted tackles. Barnes was publicly criticised by Chelsea manager José Mourinho, and said of the criticism "I found that hilarious".
On 24 May 2015, as relegated Burnley finished the season with a win over Aston Villa, Barnes was taken off with knee cruciate ligament injuries, which would rule him out for the majority of the following campaign.
Barnes said in April 2015 that he had had no further contact with the Austrian Football Association, and stated that he was open to representing either England or Austria at senior level if given the opportunity. In March 2017, whilst playing in the Premier League for Burnley, he again confirmed apparent eligibility for both England and Austria, and expressed a desire to represent the Austria national senior side. His form in the 2017–18 season led to calls in Austria for him to receive a national team call-up, and manager Franco Foda confirmed in March 2018 that he was monitoring Barnes.