EDIT: looks like on PC at least you can disco your computer from the internet then start an offline mycareer with SP. Awkward workaround with regards to a pc but I'm glad it exists.
I didn't even consider this when buying the game and now I'm seriously regretting my purchase. Can't purchase any upgrades for my player because it cant connect to the server. Somebody please tell me there is an offline only mycareer mode on PC so I can upgrade my player, and use cheatengine to bump some of the rookie starting stats.