Per the Tournament rules:
15.5. Unreleased Cards
From time to time, players will acquire cards from a new set prior to its regular release date, usually via a Prerelease. These cards may not be used in sanctioned tournaments until the regular release date of the set, as outlined in Section 16, with one exception. Cards that are already tournament legal which have been reprinted in an unreleased set may be used as long they are easily identifiable as a reprinted card. This is typically only an issue when a reprinted card receives new art, though other factors may create a similar issue. These cards should always be played with the most recent wording of the tournament-legal version of the card.