According to Amazon UK, Metal Gear Solid V: Ground Zeroes is set to release early next year.
This rumor, that was discovered by Junkie Monkeys, indicates that Ground Zeroes is not listed under the release date Dec. 31, 2014, which is traditional for games with release dates that are not confirmed. To be precise, Amazon.uk has Ground Zeroes scheduled to release on March 8, 2014. However, this should still lands under pure speculation, since Amazon US does have the placeholder release date of Dec. 31.
Ground Zeroes' possible release date follows the news earlier this week that Ground Zeroes will launch substantially earlier than its counterpart, Metal Gear Solid V: The Phantom Pain. Hideo Kojima stated that he wants Ground Zeroes released "ahead of time" to help alleviate the wait between the two titles. To further validate such an early release, Ground Zeroes was recently added to to the PS3-to-PS4 upgrade scheme; Ground Zeroes was already set to release next Spring, but signs of specific release dates help to eliminate release date delays.
We will keep our eyes peeled for confirmation on this matter, but for now, consider this pure speculation. We can confirm though, for those who haven't looked, that, whenever it officially releases, Metal Gear Solid V: Ground Zeroes will retail at $29.99 in the US and £29.99 in Europe.