The Giants’ defense has struggled this year — Tom Coughlin says he has “tremendous, grave concern” about the their too frequent defensive lapses — and each week seems to bring another bit of injury news that threatens to make things just that much harder to turn around. And so on Sunday, Justin Tuck — who’s battled neck and groin injuries already this year — played a reduced role in the Giants’ win over Dallas because of an injured big toe. Yesterday, on WFAN, he said he was awaiting the results of an MRI, and had “no idea” if he’d be available for next Sunday’s game against Washington. (For what it’s worth, he said his gut feeling is that he’ll play.) Meanwhile, in other defensive injury news, it’s at least possible that Kenny Phillips, who missed the Cowboys game, could be back on Sunday: He was able to do some running last week, but, via the Post, MCL sprains usually take at least two weeks to heal. [NYP]