• Everton have shown an interest in Lascelles and Mina • ‘I know what I have to improve. We have to sign new players’

Marco Silva has said new central defenders have been a priority since his first day as Everton manager and it is essential one arrives before Thursday’s transfer deadline.

Everton’s defensive limitations were again exposed on Saturday when they were beaten 3-2 by Valencia, their fifth consecutive pre-season defeat. Cenk Tosun and Michael Keane scored in an entertaining first half at Goodison Park and, while Silva’s attack impressed, individual errors led to all three Valencia goals.

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Jamaal Lascelles, the Newcastle United captain, has been targeted all summer by Everton, who have retained their interest despite being told the 24-year-old is not for sale. The club also enquired about Barcelona’s Colombia international Yerry Mina.

“It is not the best thing to do to wait until the last days but the market is really difficult,” said Silva, who has signed the winger Richarlison and the left-back Lucas Digne so far. “When we started we knew more or less what were our targets. I know what positions I have to improve and I have started to make more decisions to be sure about everything. But in some positions it was clear in my mind what we needed from the first day.

“Since the first day if I want to put one central defender in the game we don’t have any. Mason Holgate has been injured since the first week of pre-season. We lost others [Ashley Williams]. It is one position and it is easy to understand how many we need in that position. We have to sign new players there.

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“It is not easy for us as a club to sign some players because in normal situations they ask a lot of money and also we have to make the right decisions. We have to really improve our squad. It is not important if you change 10 players but if you bring in five or six they need to improve our squad.”

Marcel Brands, Everton’s new director of football, has started a clear-out of high-earning, underachieving players and Kevin Mirallas will be the latest departure on a season-long loan to Fiorentina providing he passes a medical. Yannick Bolasie has also been told he is surplus to requirements and could return to Crystal Palace.

However, Silva has insisted Ademola Lookman will not be leaving despite interest from RB Leipzig, where he enjoyed a successful loan spell last season. “He is our player and he stays,” the Everton manager said.