The Super Eagles had two training sessions yesterday with emphasis on building the players' stamina and adapting to the expected sweltering heat in Volgograd on Friday.
The Eagles will meet Iceland tomorrow in Volgograd, a city with a temperature akin to what obtains in the northern part of Nigeria.
According to forecasts, the weather in Volgograd is expected to be around 34 degrees Celsius, which will suit the Nigerian players.
It has been an ideal weather for the Eagles this week with the outside temperature at 32 and 34 degrees Celsius on Tuesday and yesterday.
The weather today is expected to be about 33 degrees Celsius with clear skies, which is far different from what obtained in Kaliningrad on Saturday when Nigeria met Croatia in their Group D opening game.
The team has been trying to increase the tempo of their game with emphasis on fast breaks and quick transition from defence to attack.
One of the officials told The Guardian that the team was taken unawares by Croatia and found it difficult to adjust to the tight game played by the Europeans, adding, "the coach acknowledged that it was difficult to go toe to toe with Croatia due to the quality of their midfielders and the limitations their tactics placed on the Eagles' system.
"To guard against a repeat, we have started building up the players' stamina so that they will have sufficient energy to fight for every ball throughout 90 minutes.
That is the only way we can survive because anything short of victory on Friday means the Eagles will exit the competition in the first round," the source, who pleaded anonymity said.
One of the key changes expected in the Eagles' set up is the introduction of John Ogu in place of Wilfred Ndidi in the midfield to help balance the team.
The Guardian learnt that Ndidi is still not 100 per cent physical fit, which affected his game against Croatia on Saturday.
The other changes could see Ahmed Musa and Kelechi Iheanacho coming in for Alex Iwobi and Odion Ighalo respectively.
"The coach is holding his cards close to his chest and so nobody can say for now what he intends to do. But the training sessions on Tuesday and today (yesterday) indicate that he is thinking of changing the starting line up," the source said.