Cahill added a second Premier League medal to his impressive haul this season having completed a clean sweep of the domestic and European titles in just over three seasons at Stamford Bridge following his arrival in 2012.
He made 37 Premier League starts last term as a key member of Antonio Conte's three-man defence and wore the captain's armband for the majority of the campaign.
But Pejic says he "felt sorry" for Stoke goalkeeper Jack Butland during England's recent friendly against France because of Cahill's ineptitude.
The Stoke legend added that Antonio Conte should instead be given Cahill's Premier League medal for finding a system that suited defenders who are "easily exposed".
"I felt sorry for him having to play behind a player like Gary Cahill, one of the worst defenders I've seen in one-v-one situations," Mike Pejic wrote in the Stoke Sentinel.
"He gets so easily exposed and it was him, as much as David Luiz, who needed the protection of a three-man defence in that Chelsea rearguard last season.
"Chelsea boss Antonio Conte deserves a medal - possibly Cahill's title-winning medal - for spotting so quickly that Luiz and Cahill needed such protection."