Johnson followed his former Celtic manager Martin O'Neill out of Nottingham Forest in the summer.
The Celtic defender arrived at the club this summer and is well placed to make a push towards the first-team.
The City Ground side's pre-season friendly against the Stags will now feature Forest's Under-23s.
Martin O'Neill favourite Murphy appears to have no future under Sabri Lamouchi at Nottingham Forest.
Ex-Celtic boss Martin O'Neill was sacked by Nottingham Forest last week.
Sabri Lamouchi has been named as Nottingham Forest's new manager after the Championship outfit sacked Martin O'Neill.
Martin O'Neill has been sacked by Nottingham Forest; now will Joe Lolley be on his way to the Premier League with Aston Villa?
Celtic are on the look out for a new director of football to replace Lee Congerton.
Nottingham Forest parted company with Martin O'Neill, with the Irishman lasting just six months at the City Ground.
Celtic and Rangers will resume their battle once again next season when the new campaign kicks off in August.
Christian Eriksen came off the bench to score for Tottenham Hotspur during their comprehensive win in the Champions League on Wednesday night.
If you're experiencing issues with Showbox, you're not the only one.
Arsenal defender Shkodran Mustafi scored his side's goal as they drew 1-1 with Vitoria yesterday.
Manchester City boss Pep Guardiola recently caused controversy by appearing to criticise Liverpool winger Sadio Mane.
Lucas Torreira has only started three Premier League games so far this season with Unai Emery for some reason leaving him out of the side.
Chelsea forwards Olivier Giroud and Pedro have both struggled for game time this season.
Laurens de Bock has played just two League One games for Sunderland since leaving Marcelo Bielsa's Championship high-flyers Leeds United on loan.
Tottenham Hotspur goalkeeper Paulo Gazzaniga made a crucial save against Red Star.
Rodrygo became just the fifth teenager to score a Champions League hat-trick against Galatasaray; what Premier League leaders Liverpool could have had.
Tottenham Hotspur moved into their new stadium earlier on in the year as they have had mixed results and performances on the pitch so far.