Three more players are out of Scotland's initial 40-man World Cup squad.
Injury claims Heckenberg and Lovegrove, while Calderwood called-up into England's train-on squad
Scotland's World Cup squad has been hit by more withdrawals.
Harlequins prop Daniel Heckenberg and Hull KR centre or second-rower Rhys Lovegrove have both pulled out because of injury.
Wigan winger Mark Calderwood has also been withdrawn by the Scots after his call-up into England's train-on squad.
While Calderwood is not guaranteed to make the final cut, Scotland manager Richard Thewlis said: "We only want players who are committed to Scotland so he's out of our squad."
Scotland's initial 40-strong squad had already been hit with the loss of Workington back-rower Iain Marsh with a broken arm, while Richard Fletcher (Widnes), Spencer Miller (Whitehaven) and Graeme Horne (Hull) all pulled out for personal reasons.
The final 24-man squad will be named by coach Steve McCormack on 8th October.
