The BBC are reporting today that Harris left his position at the club two weeks ago.
The Free Press has approached the club for comment.
Newly promoted Belles are bottom of FAWSL1 having lost their first three games of the season against Chelsea, Manchester City and Birmingham City.
Harris, who was appointed in 2014 and led Doncaster to promotion from FAWSL2 in his first season in charge, said last month that the club needed to strengthen their squad when the transfer window re-opened on June 3.
"We know we need to strengthen because we're a very thin squad," said Harris.
"We're a couple of players short and we need to put pressure on the players that we already have.
"Those players in my view have not quite come to the standard that they've shown in training."
He added: "If you look at the run of games we've had, we've not had the easiest of starts.
"The morale is good but when you've lost three games on the trot, it does knock your confidence a bit.
"I don't think it's a lack of belief though, I think it's just that little bit of confidence, that little rub of the green to get you going."
Belles return to action following the mid-season break at Notts County on June 26.