Brighton & Hove Albion are confident of sealing a club-record deal worth £25m for the Bristol City defender Adam Webster. The 24-year-old centre-back was a standout performer in the Championship last season, prompting Premier League interest from Aston Villa, but Brighton are confident of securing the defender after submitting an initial bid of £20m, plus add-ons.

No deal has been agreed, but any transfer is expected to eclipse the £18m Brighton paid Genk for Leandro Trossard earlier this summer.

It remains to be seen if Webster’s expected move triggers the departure of Lewis Dunk, the Brighton captain, who is believed to be of interest to Leicester City should Harry Maguire depart this summer, with Manchester United keen on the England defender.

Brighton have maintained throughout this summer that there has been no contact with Leicester over the defender. City put a £30m price tag on Webster to ward off Villa this summer. “Once big moves start happening, you wouldn’t believe the domino effect that has on all the rest of us,” said the Bristol City head coach Lee Johnson. “Webby has done fantastically well, but the market is the market. The value of the player, given a lot of the stuff that goes on in the domino effect, is always there.”

The Championship club paid Ipswich Town £3.5m, plus add-ons, for the defender last summer. City are loth to lose a key pillar of their defence, having already sold Lloyd Kelly to Bournemouth for £13m, but Johnson admitted serious Premier League interest in Webster puts the club in a difficult situation. “The burning dilemma I have is how can you stop somebody from moving for six times their wages, with a promotion in rank,” he said.

“You’re going to have to think about it, if you’re a mechanic, a dentist or for anyone. The problem for football is the sheer difference between Championship and Premier League, or League One and Championship appears life-changing. And it is really. It’s very difficult to stop somebody.”

Webster made 47 appearances for Bristol City last season, scoring three goals. The Championship club have signed Tomas Kalas – for a club-record fee of £8m this summer – and Jay Dasilva from Chelsea this summer, as well as Dan Bentley, Sammie Szmodics and Tommy Rowe.