Barcelona old boy Adria de Mesa is hoping to help pull off one of the biggest upsets in Copa del Rey history.

De Mesa played for Barca for two years as a youngster but has plied his senior trade lower down the leagues and now plays for fourth tier Barbastro.

The side from the province of Huesca in Aragon sit ninth in Group Two of the Segunda RFEF division and are preparing for the biggest game in their history when they host Xavi’s side on Sunday.

Barbastro have already claimed a LaLiga victim having beaten Almeria 1-0 in the previous round and a place in the last 16 will be at stake against Barca.

Asked about his links to Barca, De Mesa said on fcbarcelona.com: “You maybe feel it much more when you are young, that’s kind of normal, but I am a Barca fan and I always want Barca to win, except on Sunday.”

The 32-year-old knows the odds are massively against his side, and he added: “We are aware that Barca might not be firing on all cylinders but this is Barca and there is no comparison, regardless of how good our form is.

“We knew we might have a chance against Almeria, but we know that it’s one in a 100 when it comes to Barca. We will go for it if the chance arrives. We will try.”

Barca will be without Joao Cancelo, who suffered a knee injury early in their 2-1 victory over Las Palmas on Thursday.

Tests showed the defender has strained a ligament but it does not appear that his absence will be lengthy.

Xavi must decide whether to hand a first start to young Brazilian Vitor Roque, who made a lively cameo against Las Palmas following his arrival from Athletico Paranaense.

The 18-year-old is making his first foray into European football and will be keen to open his account as soon as possible.

De Mesa, meanwhile, will have no hesitation in celebrating should he do the unthinkable and score against Barca.

He said: “Who doesn’t want to celebrate a goal? Obviously I played with Barca but this is completely different. It was many years ago, youth football, nothing to do with first-team football. I am very unlikely to score but, if I do, I will celebrate. You won’t get another chance to experience such a day.”