The 33-year-old has joined the Glovers from Bristol City, after a miserable 12 months at Ashton Gate.
He arrived at the Robins, his boyhood club, last summer but hasn't featured since the 2-0 win over Scunthorpe on February 14.
City chairman Steve Lansdown said: "The move is in everyone's interest. It is not a transfer and nothing has been discussed beyond the three-month period.
"It will enable Marcus to play regular first team football at a time when he is not first choice here but also gives him the chance to show us what he can do."
Yeovil manager Russell Slade has also secured the signing of defender Anthony Jenkins, four years after he left the club to join Crewe Alexandra.
He arrived at the Robins, his boyhood club, last summer but hasn't featured since the 2-0 win over Scunthorpe on February 14.
City chairman Steve Lansdown said: "The move is in everyone's interest. It is not a transfer and nothing has been discussed beyond the three-month period.
"It will enable Marcus to play regular first team football at a time when he is not first choice here but also gives him the chance to show us what he can do."
Yeovil manager Russell Slade has also secured the signing of defender Anthony Jenkins, four years after he left the club to join Crewe Alexandra.