The Educational Institute of Scotland (EIS) said the timetable for new exams was tight and staff were still overburdened with work.
The warning on the Curriculum for Excellence (CfE) came as the EIS launched a new survey to gauge teachers' views on its implementation.
The online survey will explore key issues including access to information, advice and support, as well as resource and workload issues.
It will also ask teachers whether their school – or college – is ready to deliver new National 4 and 5 qualifications next year.
Larry Flanagan, general secretary of the EIS, said: "Feedback from our members has suggested a high degree of concern regarding the progress of the senior phase of CfE, particularly workload-related issues and the tight timetable for the introduction of the new qualifications.
"We have launched this survey to gather firm, statistically robust, evidence of teachers' and lecturers' concerns over the implementation programme.
"We support CfE and want to see it succeed, but issues such as workload, access to information and support and resourcing must be addressed to allow the CfE programme to deliver on its promise."
A Scottish Government spokesman said: "CfE will provide our young people with an education fit for the future. It is the most significant reform of education in a generation and has benefited from eight years of investment, effort and consultation with teachers, parents, and pupils."