Former England captain Rooney has flown from the United States to London for talks with the Championship club.
The deal is expected to be confirmed on Tuesday afternoon and the 33-year-old would join the club in January, after DC United's 2019 season concludes.
"It's never done until it's done," Morris told Talksport on Tuesday. "It's been a couple of days in the offing."
The former Manchester United forward has more than two seasons left on his deal with the Major League Soccer side.
"I'm confident this is something we will get sorted out," said Morris.
"The starting point was that we understood Wayne was keen to return to the United Kingdom. We had a look and decided to see if we could actually do something on the back of that.
"The key thing was conversation he had with [Derby manager] Phillip Cocu."
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