The 25-year-old was without a club after missing much of the year through injury after breaking his leg in February and has signed on a month-to-month contract in order to prove his fitness. Despit this, Jackett has no qualms about his new signing, having worked with him while manager of The Swans.
"Adebayo's a player I know well from Swansea and Watford so I know what he's about," Jackett told the club's website. "He's fully recovered from injury - he's fit and raring to go.
"Adebayo was really keen to come here and although he's signed initially on a month-to-month contract I am certain he'll prove himself worthy of a longer deal."