Bilic has now given Sakho the chance to get his career back on track in the English top flight, starting with Monday's meeting against Huddersfield Town when he is expected to play a part.
"Yeah, Diafra wanted to go. But also, that issue is not quite black and white. Did he have permission, permission on paper or just a form or an SMS? I don't know," he told Sky Sports News. "The fact is he wanted to go there. He did a medical, but the club decided not to sell him and he's back.
"So I told him 'Diafra, you are fit? I know what you can do. Sit there, hopefully now you are going to get fit and I am going to help you get focused here'. He's been training. He came back - he flew to Rennes last week, a couple of days before the end of the transfer window - but he's been training since.
"He looks good in training. Hopefully he is going to stay like that for a long time. Because he will know that, until January, he is a West Ham player. That's the way he's going to get a new contract, or play again for Senegal, or get a move - if he plays good."
Sakho, allegedly involved in a bust-up with Bilic last season, has scored 15 league goals for United in the past three years.