A control system for a vehicle, the vehicle including an internal combustion engine configured to perform automatic stop and automatic start, and a clutch configured to permit transmission of power from the internal combustion engine to wheels when the clutch is in an engaged state, the clutch being configured to interrupt transmission of power from the internal combustion engine to the wheels when the clutch is in a released state, the control system comprising: at least one electronic control unit configured to i) place the clutch in the released state and automatically start the internal combustion engine, when a request for automatic start is made and an index value is equal to or greater than a first threshold value, the index value having a positive correlation with an intensity of predicted pre-ignition, and ii) place the clutch in the engaged state and automatically start the internal combustion engine, when a request for automatic start is made and the index value is less than the first threshold value, wherein if the index value is greater than or equal to the first threshold value, the electronic control unit is configured to iii) determine whether the index value can be controlled to be less than a second threshold value, through pre-ignition suppression control for suppressing the pre-ignition, iv) a) perform the pre-ignition suppression control and b) place the clutch in the engaged state and automatically start the internal combustion engine, when the electronic control unit determines that the index value can be controlled to be less than the second threshold value through the pre-ignition suppression control, and v) place the clutch in the released state and automatically start the internal combustion engine without performing the pre-ignition suppression control, when the electronic control unit determines that the index value cannot be controlled to be less than the second threshold value through the pre-ignition suppression control.. at least one electronic control unit configured to i) place the clutch in the released state and automatically start the internal combustion engine, when a request for automatic start is made and an index value is equal to or greater than a first threshold value, the index value having a positive correlation with an intensity of predicted pre-ignition, and ii) place the clutch in the engaged state and automatically start the internal combustion engine, when a request for automatic start is made and the index value is less than the first threshold value, wherein i) place the clutch in the released state and automatically start the internal combustion engine, when a request for automatic start is made and an index value is equal to or greater than a first threshold value, the index value having a positive correlation with an intensity of predicted pre-ignition, and ii) place the clutch in the engaged state and automatically start the internal combustion engine, when a request for automatic start is made and the index value is less than the first threshold value, wherein if the index value is greater than or equal to the first threshold value, the electronic control unit is configured to iii) determine whether the index value can be controlled to be less than a second threshold value, through pre-ignition suppression control for suppressing the pre-ignition, iv) a) perform the pre-ignition suppression control and b) place the clutch in the engaged state and automatically start the internal combustion engine, when the electronic control unit determines that the index value can be controlled to be less than the second threshold value through the pre-ignition suppression control, and v) place the clutch in the released state and automatically start the internal combustion engine without performing the pre-ignition suppression control, when the electronic control unit determines that the index value cannot be controlled to be less than the second threshold value through the pre-ignition suppression control.. iii) determine whether the index value can be controlled to be less than a second threshold value, through pre-ignition suppression control for suppressing the pre-ignition, iv) a) perform the pre-ignition suppression control and b) place the clutch in the engaged state and automatically start the internal combustion engine, when the electronic control unit determines that the index value can be controlled to be less than the second threshold value through the pre-ignition suppression control, and v) place the clutch in the released state and automatically start the internal combustion engine without performing the pre-ignition suppression control, when the electronic control unit determines that the index value cannot be controlled to be less than the second threshold value through the pre-ignition suppression control..