Manchester United have not solved the defensive issues that have plagued them for years and they won't until Jose Mourinho stops playing Ashley Young at left back, according to Roy Keane.

The scathing criticism from Manchester United's former captain comes after they were beaten for a second successive away game last weekend, succumbing to a 1-0 reverse against Newcastle United.

Although they retain the best defensive record in the division, conceding just 19 goals in 27 games, Keane believes it is their frailty at the back that has seen them slip 16 points behind runaway leaders Manchester City.

Manchester United will always struggle if they continue to use Ashley Young at left back

Roy Keane has criticised Manchester United's continued use of Young in defence

'They haven't sorted out the defensive problems they have had over the last few years and that will continue,' he said on ITV.

'The two centre-halves need to do better. I've always thought with Ashley Young in your back four, you are going to struggle.'

Young, 32, has started 19 Premier League games this season with Mourinho utilising him at left wing-back depending on the system in use, but has recently started him ahead of Luke Shaw at left back.

Young struggled to maintain Newcastle United as Manchester United lost 1-0 last weekend

Explaining the decision after a recent game against Burnley, Mourinho said: 'I don't need to go to the transfer market to get a left back because I'm really happy with Luke and with the adaptation of Ashley Young so I'm really happy.

'But I think this match is a very specific one and one that you need the experience of Young and he also projects very well in attack.'

Regardless of Keane's opinion, the former England international appears to be highly valued by Mourinho after he took up the option to extend his £130,000-a-week deal by a further 12 months last November.