After a winter hiatus, Manchester United are scheduled to return to action in the Champions League this week with a knockout clash against Atletico Madrid.
Over the years, the Spanish champions have benefited from a similar strength to the Red Devils in their goalkeeping department, with Jan Oblak proving himself as an elite shot-stopper between the sticks.
The Slovenian is regarded as one of the best keepers around, and the same can be said for David de Gea, with the duo set to meet on Wednesday night.
Despite the undeniable level of Oblak, he seems to have encountered a difficult period of late. This season, he doesn't seem to be performing to his usual standard.
To capture his dip in form, Expected Goals (xG) can be applied in order to gauge some form of understanding.
xG offers an insight into the likelihood of an attempt being scored by considering aspects such as shot location, and it tends to provide an accurate summary of whether a team deserved fewer or more goals based on their shots.
Post-shot xG can be applied to goalkeepers as it specifically focuses on shots that hit the target and takes into account the quality and trajectory of the shot, thus relating to shot-stopping.
From 2017 up until the beginning of this season, Oblak was expected to concede around 124.8 goals in La Liga based on the shots on target that he faced, but the 29 year-old actually conceded just 92, excluding own goals.
That means Oblak saved shots to an above average standard, overperforming expectation by an impressive 32.8 goals.
Over the same period, De Gea also overperformed, but by 10 goals. Manchester City's Ederson is another who overperformed, but by a total of just 8.4 goals, which captures Oblak's impressive level of performance.
However, things have changed this season.
Through 25 starts in La Liga, Oblak has conceded 10.2 goals more than expected. He has underperformed xG, and by a considerable amount.
In fact, his underperformance of 10.2 goals at this stage of the campaign places him bottom of the Spanish top-flight, with the next-worst goalkeeper underperforming by just 5.9 goals.
Of the 59 shots on target that Oblak has faced this season, he's saved just 31 of them, leaving him with a save percentage of just 50.8 per cent which is the lowest across Europe's top five leagues.
De Gea, for context, has overperformed by 9.4 goals so far this season for United. His expert run of form places him top of Europe's top five leagues. No goalkeeper has saved more goals above expectation than the Spaniard.
Ahead of Wednesday's clash, the story appears interesting. The two goalkeepers are elite but based on this season alone, it is essentially Europe's most in-form shot-stopper against Europe's least in-form shot-stopper.
