Most likely not, says Google. Google has a FAQ that I have never seen before named What can I do if I'm afraid my competitor is harming my ranking in Google? The response?
There's almost nothing a competitor can do to harm your ranking or have your site removed from our index. If you're concerned about another site linking to yours, we suggest contacting the webmaster of the site in question. Google aggregates and organizes information published on the web; we don't control the content of these pages.
Our search results change regularly as we update our index. While we can't guarantee that any page will consistently appear in our index or appear with a particular rank, we do offer guidelines for maintaining a "crawler-friendly" site. Following these recommendations may increase the likelihood that your site will show up consistently in the Google search results.
"Almost nothing a competitor can do to harm your rankings..." Almost nothing. So what are the things a competitor can do to hurt your rankings?
Well, I guess if they gain access to your site somehow, they can put stuff on your pages that may hurt your rankings. But what else?
FYI - some really good relatively new FAQs posted at Google, worth a read...
Forum discussion at WebmasterWorld.