Iceland need to beat a Croatia side their coach Heimir Hallgrimsson described as being like the other half of a married couple to make the last-16.
Having drawn 1-1 with Argentina in their opener, Iceland got a rude awakening from their World Cup fairytale as Ahmed Musa scored twice for Nigeria and Gylfi Sigurdsson missed a penalty in the African team's 2-0 win.
The Iceland coach said his side got their tactics right, stopping Nigeria from managing a shot on target in the first half, only to concede two goals after the interval.
"What changed the game was the goal they scored in the second half. We had to go further forward and take more risks, and they are very good, very quick going forward, and they scored two goals like that," Hallgrimsson told reporters.
Nigeria, Iceland and Argentina can qualify from Group D, but the latter two sides need to win to have any chance of making the knockout stage, with Iceland facing Croatia in their final group game.
"We've played Croatia four times in four years, we've often said we're like a married couple -- we're trying to get divorced, but we always meet up again," the Iceland coach told a news conference.
The Croatians ended Iceland's 2014 World Cup dream by beating them in a two-legged playoff, and the relationship between the sides on the field has often been tempestuous.
"We know the scenario when we play Croatia -- it's going to be really tough games," Hallgrimsson said.
"Normally it's steel to steel, not a lot of chances, always a lot of yellow cards. In three games out of four, we've had a red card," he added.
The teams met in the qualifying campaign for Russia, with each winning at home as Iceland topped the group, but Croatia's 3-0 hammering of Argentina marked them out as one of the teams to watch in Russia.
The Croatians, who top the group on six points with Nigeria second on three and Iceland and Argentina on one apiece, may take the opportunity to rest players on Tuesday, but Hallgrimsson is taking nothing for granted.
"We were ahead of them in our group and we've already beaten them once in Iceland, so we at least have that confidence with us when we play them," he said.