According to the Cincy tweets Andy is practising on Court 5 and later on another court. So he's getting fit and also getting used to the surface.
I think we can safely assume that the knee isn't anything to get excited about but it doesn't necessarily mean he'll play in Cincy. No point in pushing himself if he isn't fit. Practising is one thing, playing in a tournament quite another. Also he must be pretty drained mentally and emotionally, and that could pose more of a problem than physical fitness.
In case anyone still doesn't know - Tsonga had to pull out because, according to his official website, he bumped into a fire hydrant in while out running in Toronto and needed several stitches in his knee as a result.
Also I don't care what anyone thinks - but Federer's constant gift of easy draws does seem to be more than just coincidence now. Having looked at Andy's in more detail, it could be worse, but he'd have to be on top of his game right from his first match.