Barnes, 25, damaged his anterior cruciate and medical collateral ligaments during the 1-0 win over Aston Villa on the final day of the season.
The 25-year-old will now go under the knife next week and is likely to be sidelined for a large part of next season and with Danny Ings set to leave the club when his contract expires next month, the Clarets will be left short of attacking options for their return to the Championship.
Barnes is the fourth Clarets player to sustain a cruciate knee injury in just over a year following fellow forward Sam Vokes, defender Kevin Long and central midfielder Dean Marney.
Manager Sean Dyche told Burnley???s website: ???They have been innocuous incidents that have ended up with four serious injuries and it???s an incredible misfortune.??
???Obviously it???s a big blow and our thoughts are with Ashley, but the irony is that our ???preventable??? soft tissue injuries have improved year-on-year.??
???To then have four cruciate injuries, you just can???t believe it.??
???However, Ashley will be looked after. He will undergo surgery next week and we know what a tough lad he is and he will be back on the road to recovery as soon as possible.???
???The positive side is that we are well rehearsed now in this type of injury and Ashley has Dean and Kevin ??just in front of him and they all have Sam to look to as someone who has recovered and is back playing again.?????