The EFL has asked Championship side Huddersfield Town to explain their team selection after manager David Wagner made 10 changes ahead of Saturday's 2-0 loss to Birmingham City.
Harry Redknapp's charges secured only their third win in 24 league games despite being reduced to 10 men after 23 minutes, with a Jonathan Grounds goal and a Craig Gardner penalty enough to beat the playoff-bound Terriers.
The win kept Birmingham out of the relegation zone but angered fellow strugglers Nottingham Forest and Blackburn Rovers due to the Huddersfield team being supposedly weaker as a result of the changes.
An EFL statement on Tuesday read: "We have today written to Huddersfield Town to request their observations in relation to team selection during their recent Sky Bet Championship match with Birmingham City.
"As per our regulations, the EFL Executive will refer the matter to the board if it is deemed appropriate to do so.
"It should be noted, however, that the result of Saturday's game will stand in all circumstances and any potential action would be taken against Huddersfield Town directly."
Huddersfield cannot finish lower than fifth in the table.
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