According to David McDonnell of the Daily Mirror, the Red Devils boss will put pressure on the club's hierarchy to spend big on players at the back, as Manchester City have done in recent transfer windows.
McDonnell added that Mourinho has lost patience with Smalling and Jones after their recent struggles, with the 1-0 loss to Newcastle United on Sunday in the Premier League a low point in United's campaign.
"The pair both signed new deals in 2015, keeping them at Old Trafford until 2019, but talks have yet to take place over contract extensions for the duo and Smalling faces being offloaded in the summer," he wrote.
United's biggest rivals have spent money to improve their defensive setups in recent transfer windows, with league leaders City making major strides in this area. As we can see, following the capture of Aymeric Laporte in January, three of City's four most expensive signings have been defenders:
United have invested in this area of the field since Mourinho's arrival in the summer of 2016. Eric Bailly and Victor Lindelof have both been signed for fees in excess of £30 million, yet the former has endured persistent injury woes and the latter has struggled to adapt to English football.
It's meant Mourinho has typically gone with Jones and Smalling. At times, the duo have performed well together, but they've creaked in recent weeks; Jones netted an own goal in the 2-0 loss at Tottenham Hotspur, while Smalling was culpable for Newcastle's goal in Sunday's defeat.
Bleacher Report's Rob Blanchette criticised the duo during the Spurs loss and encouraged United to spend big on a long-term solution at the back:
Maguire has impressed for Leicester for much of the campaign, although in recent weeks he's toiled as the team's form has dropped off. Varane, meanwhile, continues to struggle with injury issues at Madrid and hasn't quite kicked on as many anticipated.
There's no denying the Red Devils need to invest in this area if they are going to compete with City next season, though. James Ducker of the Daily Telegraph believes the defence is holding Mourinho's side back:
James Ducker @TelegraphDucker
I know Bailly is injured but I find it baffling United could have spent £615m+ since Ferguson retired in May 2013 and are still putting out a defence like that today. There are other issues but the make-up of that defence given their limitations/the outlay is quite remarkable
Despite the furore following the loss to Newcastle, United still boast the best defensive record in the top flight, with just 19 conceded in the Premier League.
However, much of that is down to the brilliance of goalkeeper David De Gea, and as we've witnessed at Spurs and Newcastle, the setup can be brittle at crucial moments. It appears as though Mourinho will have to look at adding a big-money centre-back to his ranks—for the third successive summer.