Based on this question: Can Dispel magic be used on a readied spell before the trigger occurs?
Can you Counterspell a readied spell after the turn the original spell is cast as normal, but before the trigger occurs, while you hold its energy using your concentration?
Ready (PHB p. 193)
When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration.
Note that while this and the linked question are related, as an affirmative answer to either of them would strongly imply a negative answer to the other one, they are not duplicates, as there is a possibility (which I am interested in) that both of them could have an affirmative or negative answer at the same time.
Best Answer
No
With a Ready action, the creature casts a spell on its turn and holds it until the trigger; Counterspell must be used when they cast i.e. on their turn. You can Counterspell a spell that uses a Ready action, it just has to be on the caster's turn and not after.
As an aside, because Ready uses an action, you cannot use it to cast a bonus action or a reaction spell.