Gylfi Sigurdsson
Gylfi Sigurdsson scored 10 goals and provided 13 assists in 2016-17 as Swansea avoided relegation Alex Livesey/Getty Images

Gylfi Sigurdsson has agreed to be omitted from Swansea City's matchday squad for a pre-season friendly against Birmingham City on Saturday afternoon (29 July), heightening speculation that a big-money move to Everton may be inching ever closer.

Despite playing 45 minutes and even captaining the side during a surprise 1-0 defeat at Barnet earlier this month, the Icelandic playmaker opted not to accompany his teammates on their subsequent 11-day, three-match tour of the United States. Swansea stated that he "did not feel in the right frame of mind to travel due to the current uncertainty over his future".

Sigurdsson has returned to first-team training after working with the club's Under-23s, but was not named by manager Paul Clement in a strong 21-man squad that will continue their preparations for the 2017-18 campaign with a fourth pre-season outing against Championship opposition at St Andrew's.

New signings Roque Mesa, Tammy Abraham and Erwin Mulder are all included.

"Gylfi Sigurdsson, however, will not feature as it was agreed between the club and player that he would sit this game out due to the current transfer speculation surrounding him," Swansea confirmed via their official website.

Long-term suitors Everton have already seen two offers for Sigurdsson worth £40m ($52.5m) and £45m rebuffed and it remains to be seen when or indeed if they will submit a third bid. Swansea are said to be remaining firm on their £50m valuation of a player who only signed a new four-year deal in August 2016 and is also firmly on the radar of former champions Leicester City.

"That is up to the board," Toffees manager Ronald Koeman said when asked about another approach for Sigurdsson after Thursday night's 1-0 Europa League third-round qualifying first-leg victory over Slovakian outfit MFK Ruzomberok at Goodison Park.

"Everyone knows our interest in the player but I do not decide the financial terms. It is up to the board to get an agreement with Swansea."

Everton have already spent nearly £100m on seven new recruits so far this summer, with Wayne Rooney, Michael Keane, Jordan Pickford, Davy Klaassen, Sandro Ramirez, Cuco Martina and Henry Onyekuru all arriving as the club look to push for a top-four finish and end their 22-year trophy drought.

Sigurdsson is seen as a replacement for contract rebel Ross Barkley, who Koeman is 100% sure will leave Merseyside over the coming weeks amid apparent interest from the likes of Tottenham Hotspur, Chelsea, Manchester United and Arsenal.