Who's your other PG in your seasons? Since you already have a PO Pro PG, I would think about Proing another position (if you have another PO card).
Let's say you sell CP3 in the worst case scenario for 9k (you get 6300 credits). Depending on how many credits you have now, you could potentially get another PO card for 7500-8000 depending on who it is.
Personally, I would look to make a Pro in another position.

In response to the "what should I do" questions I offer my strategy. I decided to sell all PO cards I get and only buy POTG cards. I spend no money on this game but have managed to get 5 POTG and 1 POTG Pro cards. Right now I still lose PO seasons but I am sure that as soon as I get a couple more pro POTG cards I will be unstoppable. I'm not sure if it was more efficient bypassing PO Pros. I suppose time will tell.
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