Unsworth can only be seen as cover for Leighton Baines, as the experienced defender has played at left-bacl in past seasons.
Jewell said: "With Steve McMillan injured, we didn't really have any cover for Leighton at left-back. David Wright and Emmerson Boyce can play out there if needed, but I really want two players for every position.
"He's a canny sort of player, he has great knowledge of the game at this level and most importantly, it's another body in there, who I know will give 100% every time he puts on a shirt. He's the kind of lad you want on your side, a really committed battler."
Unsworth is unavailable for selection in the FA Cup tie away at Portsmouth this Saturday, he trained with his new team-mates for the first time this morning (friday.)
Matt Jackson, who played alongside Unsworth at Everton, said: "David's a really experienced pro, and hopefully that will rub off on some of the younger lads. I know him very well and you won't find a more committed player in football. It's a good signing for the club, make no mistake."