Niko Kovac's first campaign at the helm of Bayern Munich is set to be a mixed one, regardless of how it finishes, and similar can be argued for Robert Lewandowski's season.

There is little doubt that Poland international Lewandowski has been among the world's finest strikers for many years, having led great sides for Borussia Dortmund and Bayern.

Even this season he has been excellent in most regards, scoring 33 times in 38 appearances across all competitions, but with Bayern not running away with the Bundesliga title in typical fashion and crashing out of the Champions League in the last 16, general reflection is only natural.

Lewandowski was particularly disappointing as Bayern were dumped out of the Champions League by Liverpool, making very little impact in the two legs when his team-mates would have been looking to him to make the difference, while transfer rumours linking him with Real Madrid have gone quiet.

The criticism levelled at 30-year-old Lewandowski is that his inevitable decline has started – ahead of Saturday's visit of former club Dortmund in Der Klassiker, Omnisport examined whether he has actually begun to fade.

Goal frequency not what it should be

While no one will try to claim a record of 33 goals in 38 matches is anything but excellent, using the expected goals (xG) metric, he actually should have been even more effective this season.

According to xG – which identifies whether a player should have scored based on the quality of the chance – Lewandowski has found the net four times fewer than he could statistically be expected.

That is by far his worst such record since joining from Dortmund in 2014, with his 25-goal haul tallying up exactly with xG in his first season at Bayern.

The 2015-16 season was Lewandowski's best in terms of xG (+6), and that was followed by records of +5 and +1 in the following years, showing clear signs of decline in that respect.

Less effective with big chances

One element which feeds into Lewandowski's xG drop-off and goes some way to explaining it is his converting of so-called "big chances".

The Poland striker has been presented with an average of 1.6 of them per match, the most in a single campaign during his Bayern stay.

However, he has scored 47 per cent of them, a four per cent decline from last season and also worse than the 49 per cent conversion rate he posted in 2015-16.

Bayern creating fewer chances

Although not necessarily linked to xG, it is a fact that Bayern are creating fewer opportunities this season than at any other point in Lewandowski's career at the Allianz Arena.

With 529 opportunities crafted from 40 games, that is an average of 13.2 every match, 1.3 fewer than last season and well off the 15.2 they managed in each game the campaign before.

Lewandowski could point to his own assist contribution as a caveat for not getting quite as many goals, however, as he has set up nine, his best ever return.

Still ruthless, but a long-term concern looms

Despite a decreasing xG record, curiously Lewandowski has never converted a greater percentage of his overall chances in a Bayern shirt than he is doing so this term.

Of his goal-scoring opportunities this season, Lewandowski has found the net with 29 per cent, making it his most effective campaign in that regard.

It is a four per cent increase from last season, though his average of a goal every 102 minutes is 10 minutes worse.

Despite the fact Lewandowski's overall conversion rate and goals total remain impressive, when the aforementioned sections are taken into account, it can be argued he is showing evidence of decline.

His xG record combined with the general and big-chance conversion statistics suggest Lewandowski is wasting some opportunities he should be scoring and finding the net when he might not be expected to.

While the latter element is impressive, in the long run it is unlikely to be sustainable.