Kallio, 33, who can play at centre-back or left-back, will stay at Bramall Lane until December 23 and provides temporary cover until the January transfer window.

Blackwell said: "He's a big, strong player and the reports we've had on him playing for Fulham reserves suggest he has done quite well."

Central defender Matt Kilgallon, who has not signed his new contract offer, has recently been linked with a move to Newcastle while Blackwell's defensive resources have been stretched to the limit due to injury.

Derek Geary has just returned from a 15-month absence after knee surgery, Gary Naysmith has yet to appear after cruciate knee ligament damage and Andrew Davies is scheduled to return to parent club Stoke on December 19.