I wouldn't have thought so. Whether he has breast or formula, he still needs lots more before being on solids only.

How long has it been going on for? Does he maybe have something else (!!!) brewing that is putting him off sucking/swallowing? Maybe try syringing some formula into him so he doesn't get dehydrated (or a cup if you think he can manage it)

Sorry - can't suggest anything else. If it continues maybe take him to the GP to check it out.