Can you apply polyeurethene to wood floors in 'patches'?

I've got a hardwood floor in my dining room. It's pretty worn all over, but I'm not quite ready to re-varnish the whole thing. But around the table there are a couple patches that are completely worn through to the wood (where the chairs are). Is it acceptable/advisable to put new polyeurethene down just in these patches? Or will that look bad? Thanks in advance.