FIFA Ultimate Team has been temporarily taken offline "to prepare for FIFA 14", EA has said.
The service is expected to be down until 8pm UK tonight.
The downtime is only expected to affect FIFA 13's Ultimate Team mode. Other online functionality is thought to still be available.
FIFA 14 launches on Xbox 360, PlayStation 3 and PC on September 27, with Xbox One and PS4 versions to follow later in the year.