The 20-year-old picked up the injury in a heavy challenge with Bjorn Andersson after 32 minutes of the third and final friendly of our Swedish training camp.
'Barney' was rushed straight to hospital where X-rays confirmed the worst.
It's a massive blow for last season's reserve team top goalscorer after a bright start to pre-season and a goal in our opening friendly against Falkenbergs FF on Tuesday.
Coach Chris said: "First and foremost you feel for Lee because he's away with the first team, playing in first team games and then gets injured.
"He's a whole-hearted lad and has probably gone for a challenge that a lot of players might not have.
"We're all disappointed for him because no-one wants to be injured at this stage of pre-season, particularly when the players all want to impress the new manager.
"It's been a lovely opportunity for Lee and he's looked sharp. Sometimes when the younger lads come away with the first team they end up not playing that many games but in the matches he's played, he's managed to score in one and play well.
"He's down at the moment but that's normal and it's part and parcel of the game.
"It's all about coming through this period, however long it takes and coming back stronger for it."
Chris Hughton expressed his disappointment for Lee Barnard after it was confirmed that the young striker broke his collar bone against FC Trollhattan in Sweden on Saturday.