Everton are aiming to complete a deal to sign Yannick Bolasie from Crystal Palace

Everton have agreed a deal with Crystal Palace for winger Yannick Bolasie for a fee that could rise to £30m, according to Sky sources.

The 27-year-old will become the Toffees' most expensive signing in their 138-year history providing he passes a medical and agrees personal terms on a switch.

Sky sources understand a deal to take Bolasie to Goodison Park is expected to be completed by the end of the week and will surpass the £28m Everton paid to sign Romelu Lukaku from Chelsea in 2014.

Bolasie, capped 27 times by the Democratic Republic of Congo, joined Palace from Bristol City in 2012 and helped the club win promotion to the Premier League via the Sky Bet Championship play-offs during his debut season.

Bolasie will become Everton's most expensive signing if he completes a switch to the club

He has made 143 appearances for Palace during his four seasons with the club, managing to score 13 times.

Sky sources understand Everton are hoping to conclude a deal to sign Wales centre-back Ashley Williams after agreeing a £12m fee with Swansea.

Everton are also in negotiations to sign Lamine Kone from Sunderland, with manager Ronald Koeman keen to strengthen his defensive options after allowing John Stones to join Manchester City for £47.5m.