Raul Jimenez and Diogo Jota scored in four second-half minutes at Molineux to cancel out Ruben Loftus-Cheek's deflected opener.
Sarri made five changes to the team that beat Fulham on Sunday, with Jorginho and David Luiz among the unused substitutes.
"More worrying than that it seems like his first touch has gone".
The 30-year-old Aguero is believed to have undergone tests to see if he is fit enough to feature against Chelsea, with such an injury potentially sidelining him for a maximum of two weeks.
Fans reacted to Chelsea's defeat and here are some of the best tweets.
Chelsea FC are looking to finish in the top four this season after the Blues ended up in fifth spot last term.
Sarri's regular goalscoring worries were also laid bare once more as Alvaro Morata laboured unsuccessfully for 65 minutes before being withdrawn. First team starts this season have largely been in the Europa League and have been hard to come by in the league.
It arrived with a healthy slice of fortune, however, as Loftus-Cheek's effort looked to be heading straight for Rui Patricio before Conor Coady's unwitting intervention with his head wrong-footed his goalkeeper.
A fine save by Patricio denied Willan a second goal for the visitors before a brilliant saving challenge from Ryan Bennett thwarted Willian.
The impressive Morgan Gibbs-White fed Jimenez, who had a lot to do from a tight angle but drilled the ball past Chelsea keeper Kepa Arrizabalaga.
And worse followed for Chelsea when Matt Doherty found space on the right and crossed low for an unmarked Jota to score at the far post.