Dear All, I know this may seem niaive but is it possible that one of my larger Koi has eaten a newcomer I put in the pond last week?

The 3 Large fish are around 10'' to a foot in length. and this little baby was about 2- 2.5'' in length. He was there 3 days ago hiding under a floating plant but this morning when I went to clean out the filter he was no where to be seen. I know Koi and goldfish will eat fry but this little one was surely a bit too big? There's always the hopw he's still hiding in the deep somewhere. Abit like a parent, I am responsible for his well being.