The Bombers set a club record for the number of operations at the end of last season, meaning their rehabilitation group almost surpassed the number of players able to fully train at the start of summer.
Although most players are now either back in full training or close to it, the club will remain hamstrung when picking a side for the Darwin clash with the Western Bulldogs on February 13 as many players lack the adequate preparation.
"We've got to sit down and go through it all. Anyone who's missed any substantial period of training that isn't ready to go for the first round won't play," football operations manager Paul Hamilton said on Wednesday.
"That will be a number of players but a couple of those senior guys have done a fair bit so it's likely we'll see one or two of those fellas in the side."
Among those expected to miss at least the first week are Mark McVeigh, Scott Lucas, Jason Winderlich, David Hille and Lloyd, with the skipper having some time off before Christmas with "tightening".
"Since he's come back, he's done everything and he's leading well too," Hamilton said.
"He's stepping up once again in terms of leadership and is bringing guys with him.
"He's not the sort of bloke who'll play all the NAB Cup though.
"We won't go in with anyone who's missed periods of training. That's the key thing. Anyone who is not ready for a game of football, we won't risk them.
"The Darwin connection with the Essendon football club is a long one so we want to make sure we perform, but we're not going to put individuals at risk."
The Bombers attempted to avoid the 40-degree heat on Wednesday by training at 8am at their summer base of La Trobe University in Bundoora.
However, Hamilton said while the club will remain sensible with training schedules this week during Melbourne's heat wave, it remains important to ensure the players are equipped to play in all conditions.
"You still want them to be able to cope with a little bit of heat and cope with the circumstances, because in games, there's going to be tough periods.
"Training the brain is as important as training the body so we're not going to hide from that, but we don't do anything dangerous either.
"Training earlier in the morning is good; it's not boiling yet but it is starting to warm up.
"It's not a bad thing from that point of view, but we'll try and keep away from the middle of the day at the moment."
