Here is a look back at a selection of players who have turned out for both sides down the years. How many of them do you remember?
1. OLLIE PALMER
Striker Ollie Palmer had a miserable time over his two years with Stags and moved on to Orient for an undisclosed fee. This week he became Wrexham's most expensive ever player at £300,000.
Photo: Jacques Feeney
2. JAMES ALABI
James Alabi had one of the shortest Mansfield careers ever when, as a Stoke loanee striker, he was sent off after just 32 minutes of his debut at Southend, suspended for three games and never seen again. He ended up playing 36 league games for the O's later in his career.
Photo: Linnea Rheborg
3. DARIUS HENDERSON
Former Forest star Darius Henderson was past his prime by the time he arrived at Mansfield. The former Watford, Reading and Sheffield United striker signed a three year deal with Orient on leaving the City Ground. He joined Stags in August 2016, netting once in his 13 league outings, but only started three of them.
Photo: Tony Marshall
4. WARREN HACKETT
Defender Warren Hackett played 76 league games for the O's between 1990 and 1994. He joined Stags from Doncaster in 1995 and made 117 league appearances, scoring five goals, over four years.