Shackell was replaced by on-loan Fulham defender Adrian Leijer at half-time of the midweek win over Cardiff because of hamstring trouble, while Croft left the field five minutes from time after taking a knock.
Gunn said: "Jason has very tight hamstrings. Not having played a lot of football at Wolves this season, playing Tuesday-Saturday-Tuesday has taken a little bit of a toll but it was certainly only a precaution. There is not a major injury there.
"Crofty just runs himself into the ground. You look at Lee and you could say after 60 minutes you'd look to take him off because he looks knackered. I think he did take a knock and that was the only reason he looked over to the bench. It was a precaution. The physio team will work on these guys."
Cort was rested after playing with painkilling injections but should return as the Canaries look to build on the morale-boosting win against the Bluebirds.
David Mooney capped his first start for the club with a goal and should continue while Cody McDonald will again be on the bench after scoring his first professional goal. Adam Drury (knee) could return but Dejan Stefanovic is in light training following cruciate ligament damage but will not return before the end of the season.
Plymouth's 12-goal leading scorer Paul Gallagher will undergo a late fitness test ahead of the clash.
Gallagher - who scored five goals in an unbeaten four-game streak for Paul Sturrock's Pilgrims - missed Tuesday's 1-0 defeat at Swansea through injury.
The on-loan Blackburn striker was substituted at half-time of the 2-2 home draw with Reading after suffering a tightening of his hamstring.
On-loan Manchester United centre-back Craig Cathcart, who also missed the Swans defeat through injury, must undergo a late fitness test.
Cathcart - whose replacement in central defence was Hungary international Krisztian Timar - was substituted midway through the first half of last Saturday's draw with the Royals due to a groin injury.
Defender Mat Doumbe (hamstring) is ruled out.
Sporting Life