Jose Mourinho has said Luke Shaw "has to improve" if he wants to force his way into Manchester United's starting 11

After shining at Southampton, Shaw has struggled for form and fitness at United. Credit: PA

Luke Shaw "has to improve" to get into Manchester United's starting line-up, but Jose Mourinho is staying patient as the left-back returns from his latest injury lay-off.

After shining for Southampton and playing for England at the World Cup, United made the full-back the most expensive teenager in history three years ago.

Shaw has managed just 48 appearances for United since the move due to a mixture of form and fitness issues, most pertinently the double leg break that brought his second season at the club to an abrupt halt.

The 22-year-old returned to the fold last term but Mourinho publicly questioned his attitude, application and football intelligence during a comeback campaign ended in late April by foot ligament damage.

Shaw made his latest return to fitness as a half-time substitute in Wednesday's Carabao Cup win against Burton and, while calling for improvements, the United boss showed restraint when talking about the England international compared to last season.

"He has to work, just that," Mourinho said ahead of Saturday's trip to the left-back's former club Southampton.

"You saw the game, you saw the same as I see, so are you asking if he plays tomorrow? No, he is not playing tomorrow. He has to work. He has to improve."

Luke Shaw is pushing to regain his place in the Man Utd and England team. Credit: PA

"Look, he doesn't play for six months. I am not expecting him to arrive on Wednesday and to be man of the match or to be running up and down for 45 minutes.

"It's just a process. He doesn't play for a long, long time.

"You have other players in the Premier League that in this moment who are not starting matches and their managers just say 'they're not in the best conditions'. And we're speaking about some of the best players of the Premier League.

"I heard last week the Chelsea manager saying that, I heard Arsenal manager said that. The players are not in their ideas, in their analysis, they're not in the best form after important injuries and long time without playing.

"Luke had surgery and a long time without playing football. I cannot expect him to be back and to be strong, strong, strong in his work."