Monday night's 3-0 hammering by Tottenham at Old Trafford - their heaviest defeat in four years - means United have lost two of their opening three matches for the first time since the 1992-93 season.
United failed to bring in a centre-back during the summer and Mourinho's uneasiness with the position has been evident in his team selection. The Portuguese has used two different centre-back pairings in both losses this season, and even deployed central midfielder Ander Herrera in a back three against Spurs.
The loss dropped United down to 13th on the Premier League table, and speaking exclusively to Tribalfootball, Anderson believes it is imperative Mourinho finds a solution before Sunday's trip to Burnley.
"The defending can be a lot better, [there's been] some bad mistakes and that's been their problem. It was the same in the Brighton game, the same in the Tottenham game. They have to get it right very, very quickly.
"He has shuffled his pack. If I'm honest I still don't think he knows which is his best back four, his best pairing in the middle especially. So he has to address those problems and I think Jose has to do it very quickly.
"They're 13th now and they play Burnley this weekend. That's a really difficult game and they don't want to slip any lower and the gaps getting bigger between themselves and where they want to be at the top four that qualifies at the Champions League.
"So they can't afford to have too many hiccups. They've had two already and they cant afford to have any more.
And while proponents of the 'third-season curse' theory may feel validated given United's current predicament, Anderson has advised the 53-year-old to trust his experience during this tough period.
"Listen he's got an unbelievable record for a manager and no doubt it's his toughest time since he's been manager of Manchester United.
"And my advice would be stick with what you know. You pick certain players in those positions. Pick your best players and stick with him to get some sort of continuity.
"Chopping and changing doesn't help especially in the next four, five games. Unless there are injuries to players which you can't legislate for, I would stick with my eleven and play them for the next six games."
Viv Anderson MBE was speaking to Tribalfootball to promote the partnership between 'Playonpro' and 'REDSTRIKE'.