The Dutch winger impressed Blades boss Neil Warnock while on trial at Bramall Lane, following his release from Division Two strugglers Notts County.
Cas comes in as cover for Peter Ndlovu after the club lost the services of John-Paul McGovern, who ended his loan spell with The Blades and returned to Scottish champions Celtic.
Warnock told Sheffield United's official website: "Marcel is a right winger with plenty of ability.
"He gives us cover and we will have a good look at him until the end of the season."
