Craig Cathcart has joined Watford team-mate Isaac Success in pulling out of international duty this weekend.
Cathcart, 27, had been set to link up with the Northern Ireland squad for their World Cup qualifiers with San Marino and Germany but has been forced to withdraw due to a groin injury.
The defender missed the draw with Bournemouth last time out with the problem but he should be available for the trip to Middlesbrough after the international break.
Success was expected to make a Nigeria debut but picked up a knock against the Cherries and pulled out of the Super Eagles squad earlier this week.
Watford still have eight players away with their respective nations this weekend as Nordin Amrabat, Valon Behrami, Adlene Guedioura, Jose Holebas, Christian Kabasele, Costel Pantilimon, Juan Carlos Paredes and Sebastian Prodl have jetted off for international action.