Vale agreed a transfer fee with Bristol City for the 23-year-old, who has been on loan with the side since November.
But the player rejected the Valiants' initial offer, leaving Martin Foyle to complain about outside influences.
He said: "I thought we could sort something but word got out and various people have rattled Clayton's cage.
"I offered Clayton a deal but he turned it down, so we'll have to wait until the end of the season. He has given me his word and we will speak again.
"It means I've got to start to look elsewhere. I've only got five players signed on for next year, so I'm looking to strengthen everywhere."