The Koreans will likely have to beat Norway by a huge margin in Reims on Monday to have any chance of advancing from Group A but there has been little to suggest they are capable of that.
They have played some nice soccer at times but a calamitous defence and a toothless forward line has left them with no points and no goals.
But not without hope, said Yoon.
"We have one match left here and I hope we can show everyone what we are capable of," Yoon told reporters, though conceding it was "difficult" to see how his side could get to the last 16.
The Koreans dominated possession against Nigeria, particularly in the second half, but lacked any kind of cutting edge in the opposition penalty area.
They conceded from an own goal in the first half and a lightening counter-attack in the second.
"Our players had some good chances but the end result is a loss and we need to accept that," said Yoon.
"We will have pick ourselves up and prepare for our third match. We won't give up until it's over."
(Writing by Peter Rutherford; Editing by Greg Stutchbury)
