Brian Little said: "Gary could not train yesterday and at this stage he's got to be very doubtful. Basically, you can put the injury down to the bad weather.
"We've not been able to train this week on a grass surface because of the rain. That's meant we've had to do all our work on an all-weather pitch.
"That puts extra strain and pressure on certain joints in the body. Gary jarred his back earlier in the week and he's still struggling. Obviously, it would be a blow losing such an important player but we're fortunate to have someone of Neil's calibre ready to come in.
"He's done really well since he arrived at the club. He's a smashing lad and I've no worries at all about handing him a start against Torquay. I know he won't let us down."
Fellow forward Rodney Rowe returns to full training on Monday. He suffered concussion during the Halifax match a fortnight ago in a collision. It was feared he could be out for months with a fractured jaw, but it wasn't as bad as it first looked and he could be in contention for the Macclesfield game a week today.
Dave Moore is pleased with his recovery: "Rodney was looking sharp before his injury and we've got a couple of Reserve team games next week so we expect that he will join in at some stage."
David Beresford misses tomorrow's game with a hamstring injury. It is between Andy Holt, Rob Matthews and Lee Philpott for his place on left wing, but Brian Little is giving nothing away.
"However, we do have other options. Andy came on last Saturday and did well against Rushden while Lee has looked sharp in training. He's not played much first team football recently but I know we could count on him.
"Obviously, all three are different types of players and it's a matter of deciding which is the best option."
Little's captain Justin Whittle will probably have to settle for a place on the bench tomorrow. Despite now being fully fit, Mark Greaves and Matt Wicks are expected to keep their places in central defence.
Expected line-up (4-4-2): Musselwhite; Edwards, Greaves, Wicks, Van Blerk; Williams, Johnsson, Sneekes, Matthews; Roberts, Dudfield.
Subs from: Glennon, Whittle, Mohan, Petty, Holt, Morley, Philpott, Whitmore, Alexander.