Matt Cutts, a well-known Google official has presented the answer about the whether the no-follow link can hurt site through the video at the Google Webmaster YouTube channel. No-follow link is the attribute that is used in the link tag to curb the number of directing link for following back the site.
Matt Cutt’s responded that using no-follow links will not deplete the ranking of the site, until and unless the webmaster or the user of the site are not spamming massively for getting links from another site. If this happens, then Google may take action against the spammer, despite having no-follow link enabled.
He added the following lines after saying “no, typically nofollow links cannot hurt your site”
He also gave an example of TechCrunch that many users unethically comments on the blogs for promoting concerned object, for this also a manual action will be taken for minimizing the spam.
You can see the video from Google’s Matt Cutts:
Conclusively Google official shared that there is nothing to worry about the no-follow link. The No-follow link will not affect the web crawlers in spotting the site because the Google algorithm is coded to work in such instances.