'Potential' as an adjective

It seems that 'Potential' is one of a small group of adjectives that can in fact only be attributive (part of a noun phrase). Turns out, the dictionary does indicate this:

http://oxforddictionaries.com/definition/potential

Other examples are : maximum, outright, total (in one sense), utter...

The word "potential" has two common meanings as an adjective. One is "capable of being brought into existence but not yet realized". The other is "having capability or power".

For the former meaning, your usage is correct. For example, if you wanted to express that a "potential client" was actually quite a long shot, you could describe the client as, "very potential". That is, the attribute of being merely a potential client applies to him to a greater degree than the usual potential client.

For the latter usage, you have to follow the word "potential" immediately with what the potential is. Only the adjective usage permits "potential" to be used alone.

He has a lot of potential.

He's a potential superstar.