Ifeanyi George, who played two games for Nigeria in 2017, was killed along with club teammate Emmanuel Ogbu when their car collided with a parked truck in Edo state in southern Nigeria on Sunday.
Neymar was replaced by midfielder Philippe Coutinho on Sunday after feeling an injury in his left thigh.
Nigeria will face Argentina in its final group match on Tuesday in St. Petersburg and African nation wins, it will advance to the round of 16.
Iceland's opening game of the tournament saw them hold Argentina to a 1-1 draw to give Heimar Hallgrimsson's side a fighting chance of reaching the last 16.
Croatia now lead Group D with three points and next play Argentina on Thursday in Nizhny Novgorod. Nigeria will take on Iceland a day later in Volgograd.
Nigeria has an array of attacking options that includes Premier League talent in Victor Moses, Alex Iwobi, Kelechi Iheanacho and Ahmed Musa.
England relied on goals from Gary Cahill and Harry Kane before slackening in the second half to beat Nigeria 2-1 in a World Cup warm-up match on Saturday.
Argentina, Iceland, Croatia and Nigeria are part of Group D of the World Cup.
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