Aaron Cresswell has extended his stay at West Ham by signing a new five-year contract.
Phil Jones has signed a new deal with Manchester United which keeps him at Old Trafford until June 2019.
Both Brighton and Middlesbrough have been pushing for a deal for the 25-year-old, who has one-year left on his current deal at the John Smith's Stadium.
Now Brighton have pushed ahead and are close to agreeing a deal worth in excess of £1.5million for the former Mancehster City and Leeds man.
Brighton chief Sami Hyypia targeted Clayton earlier in the summer and is now set to land one of his main transfer targets.