Ronald Koeman is said to be a huge admirer of the 27-year-old, who played in Belgium’s Euro 2016 quarter-final defeat to Wales in Lille.
The 27-year-old is attracting substantial interest after a fine season for the Hornets in which he scored 17 goals in 42 games.
Here are the latest transfer stories from around the capital:
Crystal Palace have completed deals to bring French goalkeeper Steve Mandanda and midfielder Andros Townsend to Selhurst Park.
Watford have rejected a huge bid from Shanghai SIPH for star striker Odion Ighalo.
The Eagles have enjoyed a busy start to the summer and hope to bring academy graduate Tomkins to south London.
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But Arsene Wenger is confident of acquiring his signature and bolstering his attacking options. [Daily Mirror]
From Manchester United signing megastar Zlatan Ibrahimovic to Watford rejecting a mammoth bid for Odion Ighalo, it has been a hectic start to the summer transfer window.
Palace boss Alan Pardew
While several Premier League clubs were monitoring Witsel, Everton have reportedly beat a host of rivals to the midfielder’s signature. [Squawka]
Arsenal manager Arsene Wenger
Arsenal expect to seal a deal for Japanese prospect Takuma Asano in the next few days.
And Mandanda, who is currently at Euro 2016 with the hosts, has left Marseille for an undisclosed fee. [Various]
The Belgian’s time at Anfield appears to be running out and Palace have emerged as the favourites to secure his services.
Liverpool have rejected an opening £25m bid from Crystal Palace for striker Christian Benteke.
But they will have to launch an improved offer with Liverpool hoping to recoup the money they spent on Benteke last summer. [Liverpool Echo]
Several English clubs have already set out their stalls with impressive deals while players up and down the country await news regarding their futures.
The 21-year-old international is rated as one of the hottest prospects in Japan and has gained interest from several top European clubs.
England winger Townsend, 24, sealed a £13m switch from Newcastle as Dwight Gayle headed in the other direction in a separate move.
West Ham have agreed a £12.5m deal to sell James Tomkins to London rivals Crystal Palace.
Everton have agreed a fee of around £30m for Chelsea target Axel Witsel.
The 27-year-old has made more than 200 league appearances for the Hammers but is now set to join the FA Cup finalists. [Daily Mail]
Shanghai hope to land the Nigerian international but have seen a £37.5m offer rejected by Watford. [Sky Sports]