The Lions are hoping to bounce back from their eight-wicket loss at Middleton last Saturday that saw them fall 26 points short of safety.
Horsham will be looking to pick up their first victory since their nine-wicket win at home against Brighton & Hove on June 29 and, with Cuckfield also suffering bad form, the Cricketfield Road outfit will look to capitalise and get themselves out of the relegation zone.
In the reverse fixture, the Lions lost by 15 runs and Thornely has called upon his side to repay the favour.
The Horsham captain said: “The fact that these guys are above us does make it a big game but you don’t really want to put more pressure on the guys than we need to.
“Hopefully we can turn that around and get over the line and come away with the win.
“Pretty much every game now is a must-win for us really.”