What are you allowed to do if you only have 1 card in hand, and no Canastas yet?
If the player cannot pick up the discard pile because he cannot meld the card on top, or it is frozen, then he has to pick up the top card of the draw stack, and just discard 1. He has no other choice.

He cannot play a card from his hand, unless playing that card would turn a 6-card meld into a 7-card Canasta, because he is not allowed to go out without a Canasta.

There is no rule that would allow him to play a card, and then draw another card. You only draw once per turn.