The OECD expects Spain's unemployment level to hit 27.8 towards the end of 2014, the organization said in a report published on Tuesday.
There was also a danger that the large number of long-term unemployed people in Spain could result in cyclical unemployment becoming structural, the organization said in its Employment Outlook 2013 report.
The OECD highlighted the fact that Spain's rate of long-term unemployment (12 months or more without work) had been steadily rising for some years.
In the last quarter of 2007, 19.1 percent of unemployed people in Spain had been out of work for a year or more.
But this figure had ballooned to 47 percent of Spain's jobless by the end of 2012.
"This large increase is of concern because it may be harder for the long-term unemployed to return to work because of skills depreciation and a loss of motivation leading to a rise in structural unemployment that may be difficult to unwind," the OECD said in the latest instalment of an annual report on the employment outlook among the organizations 34 member states.
The report's authors also noted youth employment had plummeted by 21 percent since the start of the crisis, or five times more than the OECD average.
They said that while some of this fall had been offset by increased enrolment in education and training, there had also been a 7 percent rise in the number of young people neither working nor studying — or ni-nis, as members of this group are known in Spain.
"Youth in this group are particularly vulnerable to having their future work careers scarred by a prolonged period of unemployment or inactivity," the OECD said in its report.
The Employment Outlook 2013 report also highlighted the fact that Spain has the second highest unemployment rate in the EU.
This was 26.9 percent in May, and second only to Greece, a country which has its nose just in front with a figure of 27 percent.
The OECD noted this meant some 4 million people had joined Spain's jobless queues since the beginning of the crisis.
The organization's Employment Outlook 2013 report also said jobless rates across the OECD will fall only slightly over the next 18 months, from 8.0 percent in May 2013 to 7.8 percent at the end of 2014.
This will leave around 48 million people out of work in the 34 OECD countries, the OECD predicted.