BBC Radio Oxford understands Oxford United are uncomfortable with the situation where Jamie Donley, Ciaron Brown, Brodie Spencer and Jamie McDonnell are all part of the Northern Ireland squad to face Wales on Tuesday. The match comes just 72 hours before Oxford host Hull City in a crucial relegation battle.
The EFL confirmed they have been contacted but stated international call-ups are governed by FIFA and selection decisions are made independently. O'Neill has previously managed Northern Ireland while working at Stoke City.