West Brom have been linked with a loan move for Ngog throughout the summer but, after his brace at Rabotnicki Kometal, Roy Hodgson said he had no intention of allowing him to leave.
Di Matteo has said he is looking at several options as he attempts to bolster his squad for the new season but he is still hopeful of agreeing a deal for Ngog.
"Ngog is a player we've been linked with and we are working on that one," he said. "We're trying. It's ongoing. We are looking at a number of players we would like to sign."