Chapman was forced off the ground in the third quarter against the Pies and was subsequently subbed out of the game.
Hird could not specify a return date for the three-time Geelong Premiership player.
“He’ll miss this week definitely, and potentially the week after, we’re not sure,” the Bombers coach said.
Chapman is the only out for the Bombers, while youngster Kyle Langford comes in for his debut.
The 191cm half forward was taken with pick 17 from Northern Knights in last year’s national draft.
Essendon has also named Elliot Kavanagh, Jackson Merret and Orazio Fantasia on the extended bench for Sunday’s clash with St. Kilda.
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