It was confirmed on Monday that the arm injury he suffered is more serious than first suggested.
Spies again suffered a bicep muscle injury to his upper arm, the same injury that sidelined him in June last year – which ruled him out for the remainder of 2013.
According to Bulls team doctor Org Strauss the player complained about pain in his bicep after the pre-season match against Stormers.
A MRI scan and ultrasound of the area was done and did not show any damage, but as the pain did not go away after the opening Super Rugby match against the Sharks, two other opinions were also called for.
These specialists found bleeding and rupture of the bicep after more scans and decided upon immediate action.
Spies will be operated on this week and will be sidelined for at least six months.
Commenting on the loss of the influential player, Bulls coach Frans Ludeke, admitted it is a setback.
“Especially as we recently just lost Arno [Botha] for the rest of the season,” Ludeke said.
“Both players are Springboks, were an important part of our game plan and contributed tremendously in the leadership category.
“However, we have learned by now that you have to adapt when the injury bogey strikes, so we will have to adjust accordingly,” Ludeke added.
* In other injury news, Strauss confirmed that Deon Stegmann will be seeing a specialist on Wednesday regarding his groin injury.
Dean Greyling sprained an ankle against the Cheetahs last Friday, but will train on Wednesday.
Morné Mellett has been declared fit, following his back strain.