Speaking on Sky Sports, Gary Neville said: "I don't think Frank Lampard is happy with Kepa Arrizabalaga. I wouldn't be. I know full well, having been in a coaching position, been in a changing room - you have to back your goalkeeper.
"You must back your players, you have to support them publicly. But privately... He conceded so many goals from outside the box last season, he's conceded another one [against Liverpool in the Premier League].
"If you don't have a top goalkeeper, you won't win that league. At this moment in time, he makes far too many mistakes. He lets too many goals into the back of his net that should be saved. That is a sorry story for a £70m goalkeeper."
On Thursday, Chelsea officially confirmed the signing of Edouard Mendy from Ligue 1 side Rennes for a fee of in the region of £22 million.
The Frenchman could make his debut for the Blues on Saturday when Lampard's men travel to West Brom in the Premier League.
