Mikel John Obi (Getty Images)
The Super Eagles are currently 47th in the FIFA world rankings - the lowest of their opponents in Group D, Argentina (5th), Croatia (18th) and Iceland (22nd).
But former Chelsea star Obi said that could spur the Super Eagles on and beyond their previous tournament best of reaching the round of 16.
"Being underdogs is good for us. It means we have to do more, we have to be humble," the experienced midfielder, who is set to play in his second World Cup, told a news conference.
He added: "We have to do better than we have ever done. It will be tough because we're in a tough group and so our first game (versus Croatia) is very important.
Nigeria were in the southeastern city of Uyo to prepare for a warm-up game against the Democratic Republic of Congo in Port Harcourt on Monday.
Obi said his side had shown fighting spirit to qualify in the first place from a tough group that included African champions Cameroon and Algeria.
"One thing that will help us is we need to be together, play as a team, and the fighting spirit we have all this time, we need to show it in Russia," he said.
"We need to continue the way we have done. We are a young and energetic team. We go as one, Nigeria and the team come first."