Gernot Rohr says his Nigeria side remain “a work in progress” and warned they “won’t get carried away with friendly success” after they beat Poland 1-0, BBC Sport reports.
Victor Moses’ second-half penalty saw off Poland on Friday but Nigeria were below par in front of a vociferous crowd in Wroclaw.
“We’ve seen a lot of good things and some things we must work on before the World Cup in Russia,” Rohr said.
“Friendly matches provide a great opportunity to see everything about your team.
“It is not really the same as a World Cup game. Our preparation is still a work in progress to be ready.
“We know winning friendly matches could give us false hope but we want to keep working hard,” he added.
They will face Serbia in another friendly in Barnet, London on Tuesday night.
Rohr has guided his team to an unexpected qualification – their sixth World Cup appearance – after taking over from Sunday Oliseh in August 2016.