Hilchos Rechilus, chapter 2, section 2

Avak rechilus (the "dust" of rechilus) is also forbidden in every situation.

If the words could be understood two ways, and you say them in a way that makes it clear the first speaker meant to put down the listener, this is certainly forbidden.

If you say the unclear words in a neutral way, it is not clear whether this is allowed. The listener may still decide that the first person surely meant to put him down.

Perhaps it depends on this: would Reuven (who is speaking now) say to Shimon (the listener) "Levi said this about you," even if Levi were standing right there with them?