More on KentOnline
Justin Edinburgh is hopeful Aaron Morris will be fit for the start of the season - but Cody McDonald and Doug Loft are likely to miss out.
Morris lasted only five minutes of Gills' final pre-season friendly on Saturday, a goalless draw against Portsmouth, before injury ended his afternoon.
But boss Edinburgh said: "We think it's just a knock. We erred on the side of caution. We thought it may have been a knee problem but, looking at it, it's just a blow to the knee and hopefully he'll be OK for Monday, Tuesday's training next week."
Captain Loft (calf) and striker McDonald (knee) missed the Pompey friendly and face a race against time to be fit for the League 1 opener at home to Sheffield United next weekend.
Edinburgh said: "Doug and Cody are progressing. We knew it was going to be touch-and-go whether they would get any game time in but hopefully they're both looking to get into training the latter part of this week.
"Maybe Saturday might come too soon but they're not too far away now."
As for the goalless draw against League 2 Pompey, Edinburgh said: "I think perhaps both teams stifled each other. There wasn't much fluency or invention.
"There was certainly good effort and endeavour but it perhaps lacked that bit of quality in the end."
On-loan Chelsea youngster Jordan Houghton was rested as a precaution, having taken a knock to his ankle against Brighton.