Chelsea's concern over the form of Kepa is well-known and his error conceding to Sadio Mane in their 2-0 defeat to Liverpool may well be the last straw.
But how do Mendy's performances from the 2019/20 season match up, and how do they compare with Kepa?
Edouard Mendy: Rennes 2019/20
The 28-year-old only joined Rennes from Stade de Reims last summer and was one of the most reliable goalkeepers in the league in 2019/20 - though he did have an excellent defence in front of him.
Mendy's 0.8 goals conceded P90 was the second lowest in the division, behind the man that replaced him at Reims, Predrag Rajkovic, while he had a healthy ratio of nine clean sheets in 24 appearances. It may be of minor concern that four of the 19 goals conceded in Ligue 1 came from corners, considering Kepa's clear lack of ability in that department.
But Mendy's Post-Shot xG of + 1.7 is far superior to Kepa's. though that would hardly be difficult, given the latter's -9.6 is the worst in the Premier League by some distance.
What does this mean? Well, post-shot expected goals is based on how likely a goalkeeper is to save the shots that they are facing. Mendy's number being positive means he has slightly overperformed, while Kepa's horror number highlights a dreadful season in which teams were scoring from all angles against him. Kepa's save % was just 54.5% - again, rock bottom of the league. Mendy in comparison was 78.4%, the third-best in Ligue 1.
Mendy v Kepa 19/20
|FC Av Rating||6.2||6.7|
|Goals Conceded P90||1.41||0.79|
But it's also worth noting that Kepa across the season faced a higher quality of shots against him than Mendy. Kepa's 0.35 PSxG is higher, by some distance, than Mendy's 0.22. This means simply that the average shot that Kepa faced was of more difficulty than those faced by Mendy.
Lampard will hope that the acquisition of Thiago Silva and Ben Chilwell can help to solidify a pretty rickety back line and hopefully make opposition forwards work a bit harder to score past the goalkeeper.
When it comes to crosses, Mendy is also better; Kepa - who conceded eight goals from corners in 19/20 - stopped just 7.2% of crosses in the season, as opposed to Mendy's healthy 10.2%.
Furthermore, Mendy seems just as comfortable, if not more so, with the ball at his feet. Both men have largely similar profiles in terms of pass completion % and also ball progression, in terms of how often the ball is sent long or played short. This side of the game wouldn't seem to be much of an issue for Mendy.
One of the main problems with Lampard spending on a replacement goalkeeper is the fact that they spent £70m on Kepa in the first place. Therefore the idea of spending in the region of that again on someone like Oblak looked far-fetched, even by Chelsea's standards this summer.
But with Mendy's fee likely to be in the region of £15m, he's extremely affordable and an upgrade on a keeper Lampard clearly doesn't trust. All in all, this could be a deal that is extremely useful for Chelsea, who are plugging many of the gaps fans were worried about.