This is very unlikely but still, one possible reason:
Make sure correct ‘Executable’ is selected in ‘Profile’ option for your Scheme. If the selected executable is ‘None’, profile option will be disabled.
In case you don’t know how to check scheme settings, you can check these setting by selecting ‘Edit Scheme’ either from Scheme menu (App name and device/simulator drop downs near the Run and Stop button ) or from ‘Product’ menu of xcode