Saving to SharePoint Online from Desktop

Hi Melissa,

Is this user a guest in your tenant, or a full fledged user in your tenant?  If he is a guest user in your tenant, I believe this is expected behavior at this time.  If not, though, there are several things on the desktop side that might be impacting his ability to save directly from Excel ranging from pending Office updates to network port restrictions or the version of OneDrive the user has installed.  If you haven't already had him try a reboot, that's always a good first step - and then you might also try repairing Office from Programs and Features.  It's also a good idea to check and see if there are any service notices in the Office 365 Admin portal that might be impacting this functionality - sometimes those things just clear up on their own!  :)