The midfielder was subbed out of Saturday's loss to North Melbourne in the first quarter and has been ruled out of this week's meeting with Carlton.
"He had an old injury there from a number of years ago and we think he has stirred that up a bit," Essendon football manager Steve Alessio told essendonfc.com.au.
"He has had the scans but we are not 100 per cent sure exactly where it is at the moment, whether it is a strain or perhaps something a bit more is going on with his foot."
"He is going to get an opinion today (Monday) and hopefully after that we will know where he is at with regards to his foot."
Leading sports medico Dr Peter Larkins said he believed Heppell had aggravated an injury he suffered in the middle of last season.
"In 2012, he had a stress fracture of his right metatarsal bone and it was sore for quite a while and then it settled down," Larkins told AFL.com.au.
"What I think has happened is the foot stress problem has recurred in recent times and he seemed to be getting sorer and sorer throughout the match on Saturday until the point where it actually got a lot worse and he had to come off.
"The question is whether he's just got really bad stress come up again or if he's actually cracked it right through,"
"If he's cracked it, he's done [for the year] for sure but if it is sore, it's not going to go away quickly either."
The Bombers are set to welcome back key forward Michael Hurley after a three-week stint on the sidelines, but Tom Bellchambers and Nick Kommer have both been sent for scans after pulling up sore from the Kangaroos clash.
The club is also managing Scott Gumbleton (hamstring) and Travis Colyer (calf) after both were unavailable for action over the weekend.
Twitter: @AFL_CalTwomey
