Summoning sickness (the rule that prevents a creature from acting on the turn it enters the battlefield under your control) is defined in CR 302.6. It restricts two specific things: declaring the creature as an attacker, and activating abilities that include the tap symbol (T) or untap symbol (Q) in their cost.
Sacrificing a creature is neither of those things. CR 701.17a defines 'sacrifice' as moving a permanent you control to its owner's graveyard. There is no rule that ties the ability to be sacrificed to summoning sickness. The creature does not need to be 'ready to act' in order to be used as a payment.
This means any cost or effect that reads 'sacrifice a creature' can be paid with a creature that entered the battlefield this turn, as long as you control it at the moment the cost is paid (CR 602.2a).
Concrete example: You cast Llanowar Elves on your turn. On that same turn you want to activate Viscera Seer's ability: 'Sacrifice a creature: Scry 1.' You may sacrifice the freshly played Llanowar Elves to pay that cost and scry 1, even though Llanowar Elves had summoning sickness and could not have attacked or tapped for mana.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.