Gillingham's 3-2 pre-season win over Bromley on Tuesday was overshadowed by an ankle injury to defender Simon King.
The 29-year-old became the latest injury worry for manager Mark Stimson to add to fitness doubts over Dennis Oli, Adam Miller, and Stuart Lewis.
"It's another bad injury we've picked up," Stimson told BBC Radio Kent.
"It's a nightmare because he's a big player for us. We knew how important he was last year and he's going to be massively important this season."
King was Gillingham's player of the year last season and was also included in the Professional Football Association's League Two team of the year.
He is so important to us that if he's got half a chance, we'll have to put him in
Mark Stimson
"I've just seen his ankle and it's huge," Stimson added.
"We've just got to shut him down for a couple of days and assess it after that and see where we go. It was a bad evening because of that.
"He's just gone over on his ankle so it's one of those things you can pick up anywhere. We just seem to be picking them up in every game we play.
"With King, he's someone who if he's got half a chance of playing he'll play.
"But it's such a long season that what we don't need to be doing is taking too many gambles early on and putting him out for a long period of time.
"But he is so important to us that if he's got half a chance, we'll have to put him in."
Stimson was however buoyed by last season's top striker Simeon Jackson, who scored on his return from injury.
"He looked really good. He's come back buzzing with confidence. It was a good 60 minutes for him," the Gills boss said.
Luis Cumbers and Mark Bentley got the other Gillingham goals.
Adam Miller has returned to training and should be ready for the start of the season, but Stuart Lewis will have another scan on his ankle injury on Wednesday.
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