Craig Cathcart has joined Liam Boyce in being ruled out of Northern Ireland's upcoming World Cup qualifiers against San Marino and Germany.
Striker Boyce's absence was expected after he sustained a knee injury in Ross County's defeat by St Johnstone.
Watford defender Cathcart has been forced out by a groin injury and that has led manager Michael O'Neill to call up veteran Aaron Hughes.
Hughes, 36, played three times at Euro 2016 to bring his caps haul up to 103.
The former Newcastle and Aston Villa defender signed for Indian Super League side Kerala Blasters after Euro 2016 but his new club's season has yet to start.
Northern Ireland are at home to San Marino on Saturday before Tuesday's game against Group C favourites Germany in Hanover.
Cathcart also missed Northern Ireland's opening qualifier last month when they earned a 0-0 draw in the Czech Republic.
O'Neill abandoned his three centre-back system without Cathcart in Prague and a flat-back four featuring League One full-backs Shane Ferguson and Conor McLaughlin kept a clean sheet.
With Wigan striker Will Grigg missing both games for family reasons, Boyce's withdrawal means Kyle Lafferty, Conor Washington and Josh Magennis are now the only three strikers in the squad.
Northern Ireland's updated squad:
Goalkeepers: Michael McGovern (Norwich), Alan Mannus (St Johnstone), Trevor Carson (Hartlepool)
Defenders: Gareth McAuley, Jonny Evans (both West Brom), Aaron Hughes (Kerala Blasters), Conor McLaughlin (Fleetwood), Lee Hodson (Rangers), Michael Smith (Peterborough), Tom Flanagan (Burton), Ryan McGivern (Shrewsbury Town)
Midfielders: Steven Davis (Southampton), Niall McGinn (Aberdeen), Oliver Norwood (Brighton), Corry Evans (Blackburn), Jamie Ward (Nottingham Forest), Shane Ferguson (Millwall), Stuart Dallas (Leeds), Paddy McNair (Sunderland), Matthew Lund (Rochdale)
Forwards: Kyle Lafferty (Norwich), Josh Magennis (Charlton), Conor Washington (QPR)