Kepa Arrizabalaga made his Chelsea debut against Huddersfield Town at the beginning of last season, with the fans in Yorkshire jeering the world's most expensive goalkeeper who had just become his club's £71 million ($91m) record transfer.
The 25-year-old was arguably at fault in some part for the first three goals at Stamford Bridge as Ajax drew 4-4 with Chelsea in a key Champions League clash.
There are also debates over whether he could have stopped goals against Wolves, Burnley and Norwich this season. Furthermore, Chelsea have the joint-worst top-flight defence away from home.
Kepa's save percentage was the worst of any top-six goalkeeper last season and that has dropped further. He has gone from saving 67.8 per cent of shots faced to only 52.5% in the Premier League.
Since joining Chelsea in 2018, Kepa ranks in 27th place out of 33 goalkeepers with a save percentage of 63.98% in the last two seasons.
Lampard's style of play may have led to the drop as Chelsea's defensive record in general has declined under the new manager. However, while they are conceding more, Kepa is facing fewer shots on target per game than he did under Maurizio Sarri.
The expected goals (xG) against Kepa last season was 37.14 in total and he conceded 39 goals in his 36 games played. That's worse this season as the xG against him is calculated at 11.92 but he has conceded 17 times in the league.
In mitigation, Kepa has lost David Luiz to Arsenal and Antonio Rudiger to injury which has led to a less experienced backline in front of him.
However, the data makes for uncomfortable reading on Kepa, who will need to improve with a seven-year £190,000-a-week deal meaning that Chelsea have little choice but to persist with him for the time being.
Kepa had the best passing accuracy of any goalkeeper in the Premier League last season at 85.4% but even that has dropped to 79% this season. This is arguably down to Lampard implementing a more direct style of play which sees Kepa producing longer, and thus more difficult passes on a regular basis.
Nonetheless, it is hard to pinpoint why Kepa's form has declined so sharply, leading him to surrender the starting shirt in the Spain goal during their Euro 2020 qualification campaign.
One reason could be that Willy Caballero has been merely an understudy with no real prospect of coming in and taking the No. 1 shirt.
"Goalkeepers pride themselves on clean sheets," Lampard said after Chelsea's first shut-out in 10 games at home to Brighton. "One of the things I’ve seen from Kepa this season from working with him is that he’s a very determined and very good professional who wants to improve.
"He goes about his work daily in a way that is very focused and I love that. In terms of confidence, his confidence shouldn’t go down. The clean sheets are not always just his own responsibility. He knows that.
"But when there have been moments this season where he feels it may have been his responsibility, he is very open to accept that fact and work to improve. I’ve been really impressed with him."