The Vikings officially placed Nwangwu (undisclosed) on injured reserve Thursday, Lindsey Young of the team's official site reports.
Sidelined since late July due to an unknown health concern, Nwangwu will be required to miss at least the first four games of the campaign now that he's on IR. Minnesota's backfield will be paced by Alexander Mattison (undisclosed) this season, with Ty Chandler, newcomer Myles Gaskin and practice-squad member DeWayne McBride backing him up.