My dad passed out hitting his head on tile floor couple of weeks ago. er ct was neg. mri this week showed 'nodule on brain'. could it be a slow bleed?

Small contusion?: It's very difficult to say what this "nodule" is without seeing images, but it is possible this may represent a tiny brain contusion, which was better detected on the mri. Slow bleeds typically occur in the subdural space and assume a more lentiform shape, not nodular, so given the limited information i would say it is unlikely to represent slow, ongoing bleed.