Cooper senior was outraged when Charlie was given his marching orders in the 39th minute following a touchline clash with Wycombe midfielder Luke O’Nien and was sent to the stands by referee Antony Coggins.
Already 1-0 down to Matt Bloomfield’s goal, Forest Green saw veteran striker Craig Mackail-Smith double Wycombe’s lead three minutes after the incident.
Substitute Jack Fitzwater halved the deficit with 20 minutes remaining but Forest Green remain bottom, one point from safety.
Wycombe nosed ahead in the 26th minute when Bloomfield converted from Nick Freeman’s cross and, shortly after the touchline melee, Mackail-Smith touched in from a Joe Jacobson corner.
Rovers had a mountain to climb after the break as Gareth Ainsworth’s Wycombe drew the sting out of the game.
Ten-man Rovers were calling for blood when Will De Havilland went into the book for a crude foul on Christian Doidge.
And they were thrown a lifeline with 20 minutes to go as Fitzwater planted a sumptuous strike beyond the sprawling Scott Brown from the edge of the box.
Fitzwater nearly equalised with four minutes to go, but his effort flew over the bar as Rovers fell to their fifth straight league defeat.
Southampton remain in the hunt for Red Bull Salzburg's Amadou Haidara and are reportedly readying a £15million offer.
Aston Villa are reportedly weighing up a summer move for out-of-favour Huddersfield defender Michael Hefele.
Southampton are lining up a summer bid for Huddersfield Town midfielder Aaron Mooy, reports claim.