Australian centre-back Downes had to come off after 65 minutes of their 1-0 defeat to Rochdale on Saturday with a head injury while midfielder Mansell needed stitches for injuries sustained at Spotland.
The pair are Shaun Taylor's only injury worries with no players sidelined for the long-term.
Rene Howe came through the 90 minutes for the Gulls after returning from suspension while fellow forward Elliot Benyon got some more game time under his belt as the Southend loanee looks to build up his match fitness.
The loss on Saturday, their fourth successive npower League Two defeat, means Torquay are only six points ahead of their Tuesday night hosts.
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