Pot odds

Since you're talking about pot odds I'll assume you ruled out flopped full house, quads.
So you have at most 12 outers (9 diamonds + 3 kings) what is cca 26% equity and you have 2:1 pot odds. So it means you need at least 33.33% to call.

But you have to think about implied pot odds here, especially since this is NL !!! I really doubt you would not be able to get more chips in if the river was another diamond or a king.
With implied pot odds it's an easy call cause you get more than 2:1 on your money 99% of the time.
Now all this is true only if you put him on top pair or overpair.
If you put him on 3 fives I think implied pot odds would also give you a call (even if you have much less equity- at most 8 outers (17%)) cause he would be willing to call larger bet on the river.
If you put him on FH or quads you're drawing dead so pot odds are not important
Flush draw is also possible but than pot odds are also not key factor for your decision.

So all in all if you decided to fold this hand because of the pot odds IMO it's wrong decision !
Unless you had a read he would fold/check behind diamond river with anything less than FH.

I forgot about implied odds

Cheers for the post, will certainly do me good to read up a bit more on the topic.