Williams is currently playing on-loan with Ipswich Town.
Parish told the South London Press: "Jonny is only going for a month initially because he is very close to our first-team. He just needs to get a bit more sharpness and play games.
"If you look at people like Wilfried Zaha and Tom Ince they have played 100 games in the Championship. Jonny has had a very stop-start last couple of years and just needs to get some games. He played very well for our U21s on Monday. He just needs to go out and play week in and week out."
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