The FPSO, originally scheduled to be complete by the second quarter of this year, is now expected at the end of next year.
In the meantime, the project is producing 25,000 barrels of oil per day via a tie-back from two of its wells to the Kikeh FPSO operated by Murphy Sabah Oil.
When complete, the Gumusut-Kakap project will include 19 wells.
Shell Malaysia chairman Iain Lo said the tie-back was an "innovative solution" that would allow production from the field ahead of the completion of the FPSO, which was being fabricated by Malaysia Marine and Heavy Engineering in Johor.
"We thank Murphy for their partnership and co-operation that has enabled this opportunity," he said.
"We look forward to ramping up the production once the FPS goes on stream."