The player will meet up with Mick Wadsworth in Portugal after deciding against remaining in this country.
Kevin Blackwell had been hoping to sign the prolific forward, although his initial offer was flatly turned down by the Potteries club.
"Contrary to several reports from the club, I can confirm that Stephen is set to sign for Portuguese First Division club Beira Mar next week," agent David Manasseh told www.stellargroup.co.uk.
"Unfortunately, he has been forced to seek a move abroad even though there were several excellent offers on the table from other English clubs.
"Port Vale seemed determined not to let him move to another English club unless they received a totally unrealistic fee.
"I suppose the good news for Port Vale fans is that the club must have money to spend if they can afford to turn down the offers that have been made for Stephen, bearing in mind that he is now leaving for nothing.
"Stephen now can't wait to get started on the next phase of his career."