BBC pundit Garth Crooks says Chelsea's decision to allow Willian to join Premier League rivals Arsenal is "madness".
The Brazilian playmaker enjoyed a stunning debut for the Gunners as he had a hand in all three goals in the comfortable 3-0 win over Fulham on Saturday.
It was not really that much of a surprise considering the Brazilian is an experienced Premier League campaigner, with 235 appearances for Chelsea before his move across London, but the Gunners taking him on a free transfer already looks a canny piece of business.
Willian was one of three Arsenal stars in Crooks' team of the week as the 2020-21 season got underway just 48 days after the last campaign ended.
And while the former Tottenham midfielder was delighted with the Brazilian's performance, he questioned Chelsea's decision to allow his contract to expire.
Writing in his weekly column for the BBC, he said: "Regular readers will know what I think of Willian as a player. I said last season that Chelsea could not afford to lose him.
"To let him go to London rivals Arsenal, of all teams, was madness and could cost them dearly in the final analysis.
"Against a Fulham side who were out of their depth, Willian produced a debut performance that must have been an agonising watch for his former manager Frank Lampard.
"The Brazilian was merely finding his bearings with a free-kick that flew past Fulham keeper Marek Rodak and hit the post. He left Craven Cottage with two assists under his belt, and a 3-0 victory.
"What have Chelsea done?"
Crooks also singled out Pierre-Emerick Aubameyang for praise, with the Gunners captain scoring a delightful goal in their season-opening triumph.
He added: "After 57 minutes, Fulham were 3-0 down at home to Arsenal, with the home side having had only one serious shot on goal.
"Meanwhile, Alexandre Lacazette, and the star of the show, Pierre-Emerick Aubameyang, showed Fulham's strikers what predatory instincts actually look like.
"Aubameyang's goal was in a different class. Come to think of it, so were Arsenal."
