The 19-year-old Packwood, who figured to play a vital role in Tab Ramos' U-20 squad that will attempt to qualify for this summer's World Cup, had to be stretchered off in the 65th minute after getting the start in the cup tie.
“I think the early diagnosis is a break to both the fibula and tibia, so it took the gloss off a fantastic performance by us," Birmingham boss Lee Clark told the club's official website. "His young teammates and friends were distraught on the pitch; in tears. I tried to get them refocused and I just said to them let’s try and win the game for Will, but we couldn’t do it.
"We were brilliant, and I thought we deserved to win the game. But we’ve lost a good young player who’s a magnificent kid. We love him to bits at the football club. He’s so honest and genuine and he’s a good pro.
"We’re going to give him the best care possible and get him back fitter and stronger next season, and he’ll have the support of everybody at the club.”