Kepa made 36 appearances in his debut season and helped Chelsea claim the Europa League.
But a growing distrust from manager Frank Lampard emerged when the Spain international was dropped for four consecutive games in February.
Now the situation has seemingly become untenable after Lampard dropped Kepa for Sunday's crucial clash with Wolves. 39-year-old Willy Caballero started instead and the Blues claimed a 2-0 victory, clinching a fourth-placed finish in the Premier League.
However, former Real Madrid and Valencia star Cañizares believes Lampard would be hard pressed to find a better goalkeeper than Kepa in today's market and should instead focus on providing him with confidence for next season.
"Kepa is a great keeper but it appears that he has not won the confidence of Lampard, which is a problem for them both," the four-time La Liga winner told Tribalfootball.com in an exclusive interview.
"It's difficult to find a better keeper in the market than Kepa and it is also difficult for Kepa to find another club like Chelsea.
"It's a disagreement that I do not understand because I believe that it is really convenient that both the club and the keeper work in the same direction and I hope that the problem will be solved soon.
"Yes, it would be a mistake for Chelsea to sell Kepa this summer. Given the current situation, this is not a summer of big transfers. They should be trying to give Kepa more confidence, not trying to sell him."
Kepa has been linked with a return to Spain, with Valencia, Atletico Madrid and Sevilla touted as possible destinations.
And while Canizares would love to see Kepa at the Mestalla, he believes his whopping €175,000-a-week contract will make any move improbable.