Thatcher is looking for a move back to the capital because his family have failed to settle in the Manchester area.
"Ben came to me a week ago absolutely mortified," said Keegan
"He has been robbed twice. It was a very scary thing. His wife would not come back."
"We love him to bits at this football club but some things are more important.
"I have told Ben he has to stay here another week because I have to find a replacement for him and I know he will not let me down.
"Some people might say I am a softy but I don't want Ben here while his family and kids are down South.
"We have done the deal but he has to have a medical and wait for me to get a replacement.
"He has made a big impression around the football club. He is a very obliging lad and we will miss him."