The Black Cats only have 22 points from 26 games.
It is understood that the deal has been agreed in principle, with Clarke Salter expected to travel to Sunderland on Sunday to finalise the switch. The 20-year-old will be Chris Coleman's first signing.
With the FIFA World Cup approaching, the former Marseille man is looking to get regular first-team action, but for Chelsea, it is believed that they will only sanction his move if an alternative is acquired.
Sunderland will hope to have Clarke-Salter signed for their next match against Cardiff City.
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Clarke-Salter made his debut for Chelsea in April 2016.
He spent time on loan at Bristol Rovers last season and Chelsea are keen for him to pick up experience in the Championship this term.
Clarke-Salter has played only once in the Premier League and just 12 times in League One; Sunderland can not afford to give him time to settle and potentially lose more matches.
He starred for England in their Under-20 World Cup win and was close to joining Birmingham on loan in the summer.
Clarke-Salter was an unused substitute for Chelsea's 0-0 draw at Norwich in the FA Cup on Saturday.