The Hammers were said to be close to signing the Southampton defender, with Craig Dawson looking to be on his way out of the London Stadium.
However, it has now emerged that Bednarek is instead joining Aston Villa on a loan deal and West Ham are set to give him a miss.
Moyes is said to have forced West Ham to backtrack on his signing and now the reason for the change of heart has been identified.
The West Ham boss gave up on the signing of Bednarek because he wanted to focus on a getting a full-back in the door.
Appropriately West Ham are now pursuing Ola Aina from Torino for their full-back needs, with Bednarek now heading to Aston Villa.
The non-signing of the Aston Villa bound man could also affect the departure of Craig Dawson, who appeared close to a move to Wolves.
It is not the first time Moyes has disapproved of a signing at an advanced stage as he also vetoed Emmanuel Dennis, who ultimately went to Nottingham Forest.