Manchester United suffered a 4-2 defeat against an AC Milan team led by former United head coach Ruben Amorim on Saturday afternoon in Poland.

United took the lead within two minutes thanks to a goal from Harry Maguire, but Milan equalised towards the end of the first half through a goal from Samuel Chukwueze.

Patrick Dorgu restored United's lead early on in the second-half, but Michael Carrick's side failed to push on afterwards, despite a host of changes at the hour mark.

Alphadjo Cissè equalised for Milan shortly after Dorgu's goal, before Goncalo Ramos and Ruben Loftus-Cheek also found the back of the net to conclude proceedings in United's final pre-season friendly before the Premier League season kicks off next weekend.

Lisandro Martinez played the final 30 minutes of the game, and while he was as good with the ball at his feet as he always is, he was poor defensively.

For Milan's fourth and final goal of the afternoon, Loftus-Cheek ran through on goal, and Martinez failed to keep up with him and cut out the chance. This is not an isolated incident. It happens very regularly that Martinez's lack of mobility costs United, especially when he has to defend in wider areas.

He is one of, if not the, best ball-playing centre-back in the world, but his weaknesses off the ball are a major issue, particularly in this United side.

United's main options for the deeper midfield roles are currently Youri Tielemans, Andrey Santos and Kobbie Mainoo. All of those players are excellent in their own right, but none of them is dominant in the air, and none of them is particularly athletic. United therefore need to compensate for this with their backline, and Martinez doesn't excel in either of these aspects.

Apart from his weaknesses, he has also had multiple long-term injuries over the last few years. Over the last three seasons, he has played a total of just 65 games for United, which is an average of less than 22 per season. That is very simply not enough, especially for a first-choice centre-back. In that position, you ideally want continuity; two players who play a large percentage of the games together. Martinez doesn't allow a head coach to do that due to his injuries.

On top of that, he only has one year left on his contract, although United can extend it for a further year till 2028. This means this is likely the last opportunity United will have to receive a good fee for Martinez, and his performances at the World Cup also mean his stock is fairly high right now.

Given his injury history, a contract extension should definitely not be something that United consider.

United have a lot of options at centre-back, but there is a real lack of quality.

Martinez and Matthijs de Ligt are both very injury-prone. In addition to that, they both have very clear weaknesses in their game and don't particularly fit this United team.

Harry Maguire is at the back end of his career, but is a decent depth option. 

Leny Yoro and Ayden Heaven are both immensely talented, but both still have a lot of developing to do.  However, Yoro has shown very positive signs during pre-season, and Heaven should start for United ahead of Martinez on the opening day of the season. 

In an ideal world, United should sell Martinez this summer and sign an elite centre-back who can help close the gap on Arsenal. De Ligt should also be sold at the earliest possible opportunity, but given he is injured and has not played since November, he will almost certainly not leave this summer.

United will not win a major trophy until they sign an elite centre-back, or until Heaven and Yoro develop into players of that quality. What is almost certain is that, as of now, the options at centre-back are not good enough to help United win major honours.