Johnstone, 24, has been linked with a £4m move to Villa's West Midlands rivals West Brom in the January window.
Manchester United have five months to make a decision over Juan Mata's future at Old Trafford even though his contract is due to expire in the summer.
Mourinho took aim at former United midfielder Paul Scholes following his criticism of Pogba's performance against Southampton.
Jose Mourinho will have the services of Romelu Lukaku for the FA Cup game against Derby County, but remains non-committal on January additions.
Sam Johnstone will be recalled from his loan spell at Aston Villa after United agreed a deal with West Bromwich Albion.
Manchester United are already without eight first team players. And now, versatile star Ashley Young has been handed a three-game ban for elbowing Southampton's Dusan Tadic.
Ashley Young will miss Manchester United's matches against Everton, Derby and Stoke after being charged with violent conduct following his elbow on Southampton's Dusan Tadic.
Antoine Griezmann is expected to join Barcelona after Manchester United's failed efforts to sign him last summer. Dybala has emerged as a priority target for Jose Mourinho.
Lucas Moura has not started in Ligue 1 and is yet to feature in the Champions League for PSG this season. The Brazilian only has two starts to his name in all competitions.
Michael Carrick's contract expires after the end of the season and the midfielder has been tipped to take up a coaching position by Jose Mourinho.
Manchester United injury list includes Romelu Lukaku, Zlatan Ibrahimovic, Eric Bailly, Antonio Valencia, Matteo Darmian, Chris Smalling, Michael Carrick and Marouane Fellaini.
Michael Carrick is set to retire after the end of the 2017/18 season when his contract at Manchester United expires.
Manchester United manager Jose Mourinho admits he cannot afford to rest Romelu Lukaku, also suggesting he won't start the Belgian alongside Zlatan Ibrahimovic anymore.
Anthony Martial and Matteo Darmian returned to training ahead of United's game against Southampton after missing the draw against Burnley.
Jose Mourinho is keen to add more potency to Manchester United's attack and has turned his attention to Dybala after ending interest in Griezmann.
Marouane Fellaini will enter the final six-months of his deal with Manchester United in January and will be free to talk with clubs outside England.
The Red Devils are 15 points behind bitter rivals Manchester City, while they were also knocked out of the Carabao Cup by Bristol City last week.
Barcelona are keen on signing Antoine Griezmann and Manchester United's decision to end their interest makes the Catalans the favourite.
Manchester United have spent close to £300m under the Portuguese manager but still find themselves potentially 15 points behind Manchester City.
Manchester United have spent close to £300m since Jose Mourinho took over but the Portuguese coach believes it is not enough to challenge Manchester City.
Fellaini, 30, is in the final 12 months of his Old Trafford contract and will be free to speak to foreign clubs from January.
Armenia international Henrikh Mkhitaryan has fallen out of favour with Manchester United boss Jose Mourinho and is expected to be sold in January.