The 21-year-old midfielder has shown encouraging signs since joining the Scottish Championship leaders on loan from Hearts in January, making seven appearances since scoring the winner on his debut against Falkirk on 30 January.
King has played against some high-quality players in his time in the Scottish Premiership with Hearts and in pre-season friendlies but he revealed that there is one who stood above the rest.
When the Edinburgh took on Everton in a pre-season match last July, England midfielder Barkley was instrumental after coming off the substitutes' bench, and King told Rangers TV that his class on the ball makes him the very best opponent he has faced.
He said: "The best player I’ve played against? We played Everton during pre-season at Hearts and Barkley came on. He is some player as well so I would have to say him."
Barkley has certainly developed into a top talent, and is enjoying the best campaign of his career this season, playing a starring role for the Premier League side.
After establishing himself as a regular in the Toffees side upon his return from loan spells at Sheffield Wednesday and Leeds United in 2012-13, the 22-year-old has taken his game to a whole new level this season.
Barkley has netted 12 goals in 38 appearances at club level in the current campaign, nearly doubling his previous season-best tally, and also netted in two Euro 2016 qualifiers for England in the autumn.