Former Huddersfield manager Clark admitted he must move players on before he is able to strengthen his squad further.
"Marlon, out of the four, he is the one who has courted the most interest," he told the Birmingham Mail. "And my last conversation with Marlon was that he was very close to agreeing with one of those clubs he is talking to.
"He gave us a certain timescale and we expect it to be concluded sometime this week. And he is understanding of the scenario, the reasons why he has to go.
"I think Marlon has enjoyed his time here, as have the other lads. But they know that if offers to them are made, then they have to be moved on."
He added: "And for me to do any more investment in the group, in terms of bringing any more players in, at least one, if not two of those lads, have to move first."
- Hayden Mullins
- Darren Ambrose