West Bromwich Albion boss Alan Pardew admits he feels sorry for Antonio Conte and believes the Chelsea manager is still missing Diego Costa.
Costa returned to Atletico Madrid for £57 million last year after scoring 20 times to fire Chelsea to the title in 2017.
They paid £60m to sign Alvaro Morata from Real Madrid as a replacement but the Spain international has scored just three times in his last 15 appearances.
Olivier Giroud also joined from Arsenal last month but Pardew believes Chelsea still feel Costa's absence.
"He's been a big miss because he's a big character on the pitch and he can change the destiny of games, not so much with his ability sometimes -- but with his character," Pardew said.
"When you've got one of those at the top of the pitch they're very difficult to replace."
Albion go to Stamford Bridge on Monday with Conte under increasing pressure during Chelsea's faltering Premier League title defence.
The Blues have suffered surprise back-to-back defeats to Watford and Bournemouth, conceding seven goals, and are 22 points behind leaders Manchester City.
Conte has also reportedly been at odds with Chelsea's board due to his unhappiness with their transfer policy.
The Baggies are bottom of the Premier League and fighting for survival but Pardew sympathises with Conte.
"I do feel sorry for the manager because the job he did last year was absolutely outstanding and I don't really think he's changed too much," he said.
"Maybe the quality of the opposition has changed and maybe the players he's had available haven't been to the consistency he had when he won it.
"But you cannot fault his record and the job he's done since he came to the Premier League.
"Chelsea had great momentum last season and they played a system that everybody was trying to deal with.
"We've all had extra time as managers to work out how to stop them so there's been a little bit of that.
"He's had injuries, he hasn't got the momentum and momentum -- that mystery word that we keep using as managers -- is such an important thing for giving confidence to everybody.''