Clayton, who is leaving Middlesbrough this summer, played with Braithwaite at the Riverside Stadium.
The 29-year-old forward was on the books of Boro from 2017 until 2019, and he failed to make a huge impact at the Championship club and had loan spells at Bordeaux and Leganes.
The Denmark international made his loan move to Leganes permanent in 2019 and was snapped up by Barcelona in February 2020 as an emergency signing for €18 million (£16.40 million) due to injuries to Luis Suarez and Ousmane Dembele, as reported by Sport.
According to Sport this month, Barcelona could be forced to sell the 29-year-old this summer due to their financial situation, with Premier League duo Everton and West Ham interested in signing him.
The Dane scored six goals and provided two assists in La Liga for Leganes this season, and scored one goal in the league for Barcelona, according to WhoScored.
While some Everton and West Ham fans will be skeptical about Braithwaite, Clayton’s comments on his former Middlesbrough teammate should be encouraging for the Goodison Park and the London Stadium faithful.