Call of Duty: Modern Warfare 4 was outed yesterday by Captain Price voice actor Bill Murray, who suggested voice work had already begun. However, Infinity Ward has now shot down the actor's involvement and denied that voice work has begun - but hasn't denied the game's existence.
Infinity Ward took to Twitter last night to debunk the voice acting rumour, along with the message: "Interesting news today, but it's not true. We've not talked with any voice actors, so all news is speculation."
Note that the game itself hasn't been debunked.
VG247 asked Activision for comment on the game's existence yesterday, but has so far received no reply.