The Everton and Manchester United legend shocked supporters at Pride Park by announcing his departure from the club with the League One side in administration and in search of a new owner following their relegation to the third tier.
Rooney, who has led the club through the bleakest of times with the club handed a 21-point deduction leading to relegation last term, said that his time at the club 'has been a rollercoaster of emotions, both highs and lows', but insisted that the Rams now needed 'fresh energy' for the challenge ahead.
The 36-year-old has stayed loyal to Derby despite links with clubs such as Everton in the last year, and according to Bent, Rooney should be proud of everything he's done to help the club.
Speaking on talkSPORT Drivetime, Bent said: "It's come as a bit of a surprise but when you look at what he's had to deal with since he got that job - the points deduction and going into administration.
"He's had that much to deal with and I think he can walk away from this job with his head held high.
"Of course Derby fans would have wanted him to stay. He did a great job there, showed great dedication when he was linked to other jobs but he decided to stay.
"He thought he could get that crop of players out of the relegation battle, but it wasn't to be and he said it in his statement, the club needs fresh energy and a new approach because it's different.
"The Championship's a different league, League One is an incredibly hard league to get out of and they still haven't sorted the buying situation.
"Unfortunately for Derby, my former side, it's still one big mess.
"He's going into the season and thinking what money has he got to spend, what players are going to be staying, what players can he give new contracts too.
"It's a complete mess at the moment.
"For Wayne, the administrators are the ones to blame because they had Chris Kirchner in there and I don't know quite what's happened, but you get to this point and he'll be thinking 'what more can I do?'.