Algeria have qualified for the last 16 for the first time but will face a sterner test than most when they face Germany tomorrow morning (Singapore time).
The Algerian team will nearly all be fasting when they battle the Germans in Porto Alegre. Muslims fast from dawn to dusk during the month of Ramadan, which started yesterday.
The Algerians are using Hakim Chalabi, a sports medicine specialist at the Aspetar clinic in Doha and one of Fifa's leading experts on fasting footballers to help them.
"It is a period when the risk of injury increases, especially in the lower back, the joints and the muscles," said Chalabi.
"This is mainly because of dehydration and not the lack of eating."
Players can lose up to six litres of fluids during a match.
The expert, a former medical chief at French football giants Paris St Germain, said the level and quality of nutrition had to be changed to cope with exercise during Ramadan.
"The players must hydrate themselves better. We also advise them to take a longer siesta during the afternoon to make up for some of the lost sleep."
Muslims have to get up very early in the morning to pray before starting their fast.
Algeria's captain Majid Bougherra (above) confirmed drinking enough is the most difficult part.
"But we are okay. The climate is good," he said.
"Some players can delay the fasting. In my case, I am going to do it in line with my physical state. But I think I am going to do it."
Chalabi said there could also be a psychological boost during the fasting month.
"Curiously there are some athletes who have better results during Ramadan because they really want to do the fast," said the doctor.
Religious authorities in several countries take a pragmatic attitude to football and Ramadan.
In 2008, the Dar al-Ifta, Egypt's main Islamic body, allowed professional footballers to eat during Ramadan if they were bound by contracts to play during the holy month and they felt that fasting will impact their performance.
Other workers involved in "hard labour" are also given a dispensation.
Germany's Mesut Oezil said he falls into this category.
"I can't take part," said Arsenal's attacking midfielder, who added that the World Cup is "working".
"It will be impossible for me to take part this year."
Another player who is not fasting is France defender Bacary Sagna.
"As a Muslim, I know some laws allow you to avoid fasting," said the player who is of Senegalese origin. "I will not fast, but I respect those who will practise it." - AFP.