Highlights: Uruguay 1-3 Costa Rica

As Costa Rica's players tie their laces and the team's coaches shout final instructions before Sunday's World Cup last-16 tie with Greece, Arsenal striker Joel Campbell will pause, take a breath and begin whispering to himself.

"The Lord is my light and my salvation; whom shall I fear? The Lord is the stronghold of my life; of whom shall I be afraid?"

He recites the words to give him strength, words that make him think of his mother, Roxana, his father, Humberto, and three siblings in Costa Rica. Family is the second pillar in his life. God is the first.

Campbell (left) scored for Olympiakos in a Champions League first-leg victory over Manchester United in March

If Psalm 27 has given Campbell the conviction to play without fear, whoever the opposition, that fearlessness has also become a feature of the way Costa Rica have played in this World Cup.

The Central Americans have already upset the odds by topping a group containing three former World Cup winners in England, Italy and Uruguay - and it has been Campbell who has provided the stand-out performances, notably in the 3-1 win over Uruguay.

Highlights: Italy 0-1 Costa Rica

But for all the plaudits the 22-year-old has received in Brazil, he remains something of an unknown quantity to fans of his parent club.

It was back in 2011 that a teenage Campbell signed for Arsenal from Costa Rican side Deportivo Saprissa - but he has still to play a game for them. Having been denied a work permit when he first joined the Premier League side, Campbell was loaned to Lorient in France and Real Betis in Spain before a spell at Olympiakos in Greece.

In fact, his only appearance in England to date came for the Greek side last season, when he took on Manchester United in a Champions League last-16 tie in March. Three weeks earlier, he had announced himself with a 25-yard strike in the first leg.

But Arsenal fans may grow more familiar with him soon - on the strength of his performances for Costa Rica, he has now been granted the right to work in the UK.

Who is Joel Campbell? Born in the Costa Rican capital San Jose, Campbell played for the country's most successful team Deportivo Saprissa for two seasons

Appeared for Costa Rica in the Concacaf Gold Cup, Copa America and the Fifa Under-20 World Cup

Scored his first international goal for his country in the Gold Cup against Cuba, as Costa Rica reached the quarter-finals

On 19 August 2011, Arsenal confirmed they had signed Campbell, but he had failed to obtain a work permit to enable him to play in England

Paulo Wanchope, Costa Rica's assistant manager, says the young striker is desperate to play for the Gunners, where he has two years remaining on his contract.

"Joel really wants to go back to Arsenal and play," the former Derby, West Ham and Manchester City striker said.

"I told him that the only way to do that was by performing well on the pitch at this World Cup. He has done well, but he can perform even better. Arsene Wenger is watching him."

Indeed he is. The Arsenal manager has already said he wants Campbell at pre-season training, having been impressed by his direct running and willingness to shoot on sight against Uruguay.

So what can Gunners fans expect if Campbell lines up at Emirates Stadium next season?

There is a steel behind the raw talent that marks Campbell out as a force to be reckoned with. He was born in San Jose, the capital of Costa Rica, but his family is from the English-speaking area of Limon, which explains the Scottish surname. The third of four children, he grew up surrounded by football, fighting to be noticed.

Campbell has been granted a UK work visa on the strength of his performances for Costa Rica

As a youngster, he would juggle empty cans on the street. On one such occasion he was spotted by then Costa Rica manager Ricardo La Volpe. The national side were playing friendlies close by and, while his friends bought tickets to go to the games, Campbell told them all he wanted to go, but as a player. A few weeks later, La Volpe called him up to the Costa Rica national team.

"Who is Messi? Who is Neymar?" the manager said at the time. "Gentlemen of the press - I present to you: Campbell. I discovered him playing with cans."

Those who have worked with him talk about his dedication in training, his work ethic, his desire to get better and better. They also talk of a confident, calm young man - a winner.

Did you know? Campbell bought 100 packets of World Cup stickers trying to find one of himself. None of the 500 was of him.

"I've always said you have to think about winning," his father Humberto said. "I've always said that success goes hand in hand with sacrifice. We get him to set goals."

His immediate goal is to take Costa Rica to further success at this World Cup,

"We always believed we could do this," Campbell said. "Football is not decided by the shirt you are wearing. With work and effort, you can win against anyone. We are very satisfied, very happy with what we have achieved but we will keep working to do more."

His life is changing on and off the field. He celebrated his goal against Uruguay was by tucking the ball up his shirt, a nod to Maria Fernanda Cascante, his pregnant girlfriend.

"I dedicated my goal to my family, my girlfriend and our child. Was it the most important goal of my life? I hope that is still to come," he said.

"This is unforgettable. We are part of history. Nobody would have put a dollar on this team qualifying but there you go. It can change football in Costa Rica.

"These are the best days of my career."

So far. Better days may yet lie ahead.