according to BBC first choice goalkeeper, Danny Coyne is out as well as striker, Andy Gray. http://news.bbc.co.uk/sport1/hi/football/eng_div_1/6200251.stm this page also says that Barnsley have no injury worries which suggests that Howard's injury is not particularly serious.
According to "The Championship" on Sunday they only had 16 fit first teamers to pick for prior to their game at the weekend and picked up an injury in that game.