Ole Gunnar Solskjaer acknowledges Manchester United must sharpen up in defence if they are to achieve their ambitions of winning major trophies. 

United eased into the last 16 of the Europa League on Thursday after a goalless draw with Real Sociedad at Old Trafford secured a 4-0 aggregate victory. 

It was their 16th clean sheet in all competitions this season, the third-most of any Premier League team, behind only Chelsea (19) and Manchester City (24). 

However, conceding goals has been a problem throughout 2020-21. The Red Devils have shipped 46 across all competitions – more than twice as many as City (20) – with 32 of those coming in the league, more than any other side presently in the top five. 

Although 11 of those were conceded in United's first three league matches of the season – an aberration Solskjaer put down to a lack of pre-season preparations – their defensive frailties have cost them valuable points despite scoring 53 goals, the most in the top flight, and 85 in all competitions, as many as rivals City. 

Ahead of Sunday's clash with Chelsea, who are unbeaten under new head coach Thomas Tuchel, Solskjaer highlighted the need to become more resolute at the back in order to close the gap to Pep Guardiola's men, who are top by 10 points.

The United manager told reporters: "We're on a good path. We feel we have improved but we're nowhere near where we want to be, and that's higher up the table, winning trophies. So, the hunger in the group and the mentality in the group is good, and that's the main thing now: that we keep on improving. 

"We know we've scored quite a few goals; of course, we need to be a better team defensively. 

"Certainly, the amount of goals we've conceded, even though we had 11 in the first three games, those three games almost don't count in my head because we were so far away from a Man United team in the preparation, no pre-season. 

"Even then, we've conceded too many goals, so we need to improve on that, definitely. And win tighter games: we've had many games against, you know, City, Chelsea, nil-nil, Liverpool nil-nil, so get the goals in those games. 

"We just have to focus and tick one game off at a time. The [next] three games are massive. We've got Chelsea just behind us, City a way in front of us, and we can't let them run further away if we have ambitions of catching them and we can't give Chelsea too much hope of catching us, either. 

"It's still 38 games for every team, so if you get a run, either good or bad, it might impact you. Of course, as a group and a culture, bouncing back for us after a couple of setbacks we've had, it's an important period. 

"But our group mentality is really good, and we look forward to these games. We know Thomas has come in, it's changed a little bit at Chelsea, so it's going to be a great challenge for us. 

"You can see the results, the stats, the possession they've had. They keep teams away from their goal, keep the possession. He's done really well. 

"It's never easy coming into a season halfway through, so he must be pleased as well. Hopefully, we can stop that run. That's my job now." 

With captain Harry Maguire rested, Eric Bailly produced a strong performance against Sociedad alongside Victor Lindelof, making three clearances and winning all four of his contested duels. 

"Both of them played well, so Eric and Victor and Harry, three very good centre-backs that I can rely on, and Axel [Tuanzebe] as well. I've got four to choose from," said Solskjaer, who has a decision to make for his team against Chelsea. 

"Sometimes it's the opposition, sometimes it's the form, sometimes it's little things. I think the two of them will keep on playing and they might be playing together as well." 

Anthony Martial endured another goalless outing, producing only one shot on target. The 25-year-old has now failed to score in 14 of his past 15 appearances in all competitions and has not found the net in his six games since scoring twice in the 9-0 demolition of Southampton. 

"Anthony knows what we want and Anthony's working really hard to do well for the team. That's what's pleasing me," Solskjaer added. 

"I see him every day in training. He's not going to sit down and wait for things to happen; he knows he has to make things happen for himself. 

"We encourage him, coach him, and we know he's got this quality and class. Everyone goes through a little difficult patch at the moment, or at times, and Anthony, I think we saw tonight, he's working harder and that's the main thing."