The Bosnian has emerged as the Blues' top transfer target up front after an approach for Andy Carroll was scuppered by an injury to the striker.
Goal understands that Roma and Chelsea have struck a deal for Dzeko, but that personal terms have been harder to agree so far.
Chelsea are reluctant to break the bank on the salary of a player who will turn 32 in March, frustrating efforts to seal the transfer.
Another complicating factor regards Dzeko's agent, who is yet to obtain a visa to visit the United Kingdom in order to continue talks.
Fellow Chelsea target Emerson, meanwhile, starts from the bench.
Dzeko is the club's top scorer this season with 12 goals in all competitions, helping the Giallorossi to fifth place in Serie A.