It has been widely reported that Louis van Gaal has made Powell available for transfer in January and the midfielder has been linked with a loan move to Preston North End over the past few days.
Due to his impending departure, many felt that Powell was left out of the Under-21 squad on Monday but Martin has gone on to address the speculation by attributing the 21-year-old's absence to a calf problem.
Martin said: "He's injured. He's got a calf strain at the moment."
Powell's injury may place his possible shift to Deepdale in doubt as the Lilywhites look to bring in reinforcements quickly in a bid to strengthen Simon Grayson's squad who sit 10 points out of the playoff places.