Middlesbrough forward Jonathan Franks is set to be sidelined for around three months due to a back problem.
The 20-year-old has a herniated disc and is now expected to undergo surgery in the next couple of weeks.
While Franks did not feature in the Championship opener against Ipswich over the weekend, Gordon Strachan has confirmed he would have been involved in Tuesday's Carling Cup clash.
"I would have included Franks against Chesterfield but he is another one who is going to be out for a long time because he needs an operation on his back," Strachan told the club's official website.
Franks' injury is the latest setback to hit Boro after Willo Flood was ruled out for six months with a dislocated knee.
Andy Halliday and Gary O'Neil are also out for the match with Chesterfield due to injury, while Kris Boyd, Stephen McManus, Barry Robson, Kevin Thomson and Tarmo Kink are on international duty.