Reynolds, 21, has yet to play for the champions due to stiff competition at Leigh since joining from Castleford last October.
However, he should get plenty of game time with the South Yorkshire club, who are still seeking their first win of the Championship season.
He was the joint winner of the Championship One Young Player of the Year award while on a dual-registration contract with York City Knights last term.
Goal-kicking Reynolds can also play half-back and Doncaster coach Paul Cooke is likely to pick him for this afternoon’s trip to second-bottom Whitehaven as he starts a month’s loan.
He said: “Ben is a player I have kept my eye on. He was the young player of the year last season in Championship One with York City Knights, which led to Leigh signing him. Ben needs to play; he is a very good player with a lot of talent and he will definitely add something to the group during his initial month with us.”
Leigh head of rugby Derek Beaumont added: “Ben is a great lad who has quickly become a favourite within the camp.
“We need Ben to be playing at a high level to maintain his progress and intensity and Doncaster is a good place for that.
“Paul Cooke will, no doubt, be able to add to Ben’s experience; they have an excellent playing surface and are a very good club with a good leader in Carl Hall.
“Ben will still maintain his full-time regime here where we are confident he has a long future.
“Paul Rowley will monitor his progress and he’ll be able to push for a place in our team while working hard at Doncaster.”
Reynolds played four Super League games for Castleford and, therefore, should bolster struggling Doncaster who have lost 11 successive matches dating back to last September.