But now the England midfielder, who will face his boyhood club Everton on Sunday for the first time since leaving Goodison Park for Chelsea, he has overtaken Ruben Loftus-Cheek in the Stamford Bridge pecking order.
The battle for places in Sarri’s midfield is intense with Jorginho, N’Golo Kante, Barkley, Loftus-Cheek, Mateo Kovacic and Cesc Fabregas all fighting for places, and Danny Drinkwater out in the cold.
But Barkley, after a start which Sarri describes as far from perfect, has worked hard and made himself a real contender – an effort which has also seen him recalled by England.
Barkley played the entire 90 minutes as Chelsea took their unbeaten run this season to 17 games by reaching the last 32 of the Europa League with a 1-0 win at BATE Borisov on Thursday. Sarri’s side are now the only unbeaten team in all of Europe’s top five leagues.
Barkley joined last January in a £15million deal, but due to hamstring problems it is only this term that the 24-year-old has started to thrive, and has hit three goals in his last five games.
But Sarri admitted: “At the beginning, in the first month, Ross was in trouble.
“But then he started to improve in every training session, in every match. I am surprised how he has adapted if I think back to the first month, but not if I think of the last two months.
“At the moment from a tactical point of view Ross is a step ahead of Loftus-Cheek. Because Ruben in the first part of the season had two or three little injuries.
“I like Ross very much. He is a complete player. He has physical qualities, he is fast. Technically he’s very good. He kicks well with his left foot and his right. He’s improving in moving the ball.
“He has become mentally quicker, and he is improving tactically. He is on the way to becoming a very important midfielder, not only for us but for England.”
Sarri will make a host of changes again for the visit of Everton after one of the poorest performances under his command in Belarus. And Loftus-Cheek could be a doubt after picking up a back problem.
Eden Hazard, also recovering from a back injury, is almost certain to start after getting another hour of football under his belt in Belarus, where Olivier Giroud’s first club goal of the season earned Chelsea qualification.
But Sarri warned: “Eden is doing very well with his back, but now he needs to improve his physical performance. He did not play badly, but he can do better. I’m not sure if he is ready for 90 minutes yet.”