Michael O'Neill has expressed his frustration after discovering that several Championship clubs approached the English Football League about his combined role as Northern Ireland and Blackburn Rovers manager.
The 56-year-old expressed particular dismay that no club official contacted him personally before escalating their concerns.
Following Tuesday's 1-1 draw with Wales in Cardiff, O'Neill said: "If I'm honest, I'm a little bit disappointed.
"These clubs ask for references on players. They ask for character references, level of performance, from us and our staff when they want to sign these players."
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He emphasised that the footballers in question held international status when their clubs recruited them, questioning why this had suddenly become problematic.
O'Neill added: "I didn't get a phone call from any of the managers."
The friendly at Cardiff City Stadium saw O'Neill deploy several players from clubs battling alongside Blackburn against the drop, while his own young defender received minimal involvement.
Oxford's Jamie Donley opened the scoring in the 22nd minute before being withdrawn after 64 minutes, with teammate Ciaron Brown also playing an hour before making way for fellow U's player Brodie Spencer.
Michael O'Neill has expressed his frustration after discovering that several Championship clubs approached the English Football League
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West Brom midfielder Isaac Price completed the first half, whilst Portsmouth's Terry Devlin remained on the pitch until the 80th minute.
By contrast, uncapped Blackburn teenager Tom Atcheson entered the fray only in the final 10 minutes to earn his international debut.
O'Neill said: "If you look at the players in question, you know Isaac played 45 minutes tonight, Ciaron played 60, Jamie played 60. I'll always try to protect the players."
The accusations of a conflict of interest emerged after O'Neill named six players from Blackburn's relegation rivals in his 22-man squad for the international window.
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The friendly at Cardiff City Stadium saw O'Neill deploy several players from clubs battling alongside Blackburn against the drop
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The U's were understood to be among those who raised the matter with the football authorities, having seen four of their players selected just days before vital league matches.
Portsmouth and West Bromwich Albion, both locked in the same survival struggle, also had representatives called up in Devlin and Price, respectively.
The EFL confirmed that "one or more clubs" had made contact but stressed that international call-up policy falls under Fifa's jurisdiction rather than their own.
However, the league added that it expected all selection decisions "to be taken with integrity and in a way that does not bring the game into disrepute".
Michael O'Neill serves as Northern Ireland and Blackburn Rovers manager
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The Championship standings paint a stark picture of the survival battle facing all parties involved.
Blackburn currently occupies 19th position on 43 points, separated from West Brom solely by goal difference after the Baggies accumulated an identical tally.
Portsmouth sit precariously in 21st place with 40 points, whilst Oxford and Leicester City find themselves trapped in the bottom three on 39 points apiece, the latter having suffered a six-point deduction.
Sheffield Wednesday remain rooted to the foot of the table on minus six points following an 18-point penalty.
The next round of Championship fixtures takes place on Good Friday, with West Brom travelling to Ewood Park on Monday, a pivotal encounter between two sides level on points.
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