The 23-year-old arrived from Oxford United after a goal-laden season in League Two.
Sunderland could bring in a number of new players in the weeks ahead.
The US Under-23 international midfielder got his first extended taste of senior football on loan at Rangers last season.
Serie A side Lazio are keen on the Frenchman's signature.
Valencia has rapidly fallen out of favour at the Hammers under Slaven Bilic and looks set to complete his exit.
The Reds have spent heavily on improving their forward options this summer.
The Tottenham Hotspur boss will not be bringing in any more central defenders this summer.
Warburton has been a hit at Ibrox since taking charge last season.
Leeds United have been linked with some interesting targets in recent days.
The Swedish star could feature in the Red Devils' match against Galatasaray in Gothenburg this Saturday.