Kris Commons has told Barcelona that it would be "very unprofessional" of them to underestimate Celtic when the two sides meet in the Champions League.

Barcelona will return to Celtic Park on Tuesday evening, where they were beaten 2-1 by the Scottish side in last season's group stages.

Despite losing 1-0 to Greenock Morton in the third round of the Scottish League Cup on Thursday, Commons has said that Celtic will be ready to face Gerardo Martino's side.

"It is going to be difficult but I think it will be very unprofessional of them if they didn't think that we were a threat," Commons told STV.

"I know we got beat by Morton the other night but they will be looking at footage of us playing against AC Milan and how well we did there and probably showing our own strengths and weaknesses.

"They obviously now have Neymar who is one of the best players in the world so attacking wise, they will be a bigger threat [this year]. But for us, it is about staying focused and trying to repeat what we did last year. We certainly got some lady luck last year so we will be looking for a bit more of that."

Celtic lost their first match of this season's group stages 2-0 to AC Milan.