The Leeds defender has left Elland Road for Derby.
Warnock was enjoying a fine season at Elland Road, statistically outshining many of his Leeds team-mates.
Now, however, Derby have announced the 33-year-old's signature.
Cooper's reaction has involved wishing Warnock luck during his time at Derby and thanking him for his service to United, along with a compliment about his professionalism.
Leeds boss Redfearn had suggested during his press conference earlier today that Cooper could be 'captain material' at Elland Road.
Warnock had captained the side during his time at the Yorkshire club, while Jason Pearce started the season as skipper.
On the pitch, Leeds face a tough test against in-form Birmingham City on Saturday afternoon, with Redfearn's men hovering dangerously close to the Championship relegation zone.
Youngster Charlie Taylor will likely deputise for Warnock again when facing Gary Rowett's side, while the 33-year-old's new side Derby play Nottingham Forest in Saturday's early kick-off.