You mean the actual original web site inside the TT-RSS preview pane? Sort of.
You could code a plugin to do it but because of various security policies with browsers and web sites, you’d probably find it wouldn’t work on many sites. You’d need to proxy the content through your TT-RSS server to make it work reliably; this would introduce a bunch of other security problems that I’m not going to go into.
In short, if you know what you’re doing you could do it. I would recommend avoiding it though.
You would be much better off using the af_readability or feedmod plugin to get the article’s full content. These plugins will better handle sanitizing the information.