The Milers arrived on Saturday for a seven-day camp which includes a behind-closed-doors friendly against Fleetwood Town.
Paul Warne's side have added Conor Washington, Tom Eaves, Jamie McCart, Peter Kioso and Cohen Bramall to a squad which will be back in the Championship next season but further upgrades are needed, especially with star players Michael Smith and Michael Ihiekwe joining Sheffield Wednesday at the end of their contracts.
Warne places huge value on the fitness work he does in pre-season, so is keen to see deals done as quickly as possible.
Stewart spoke to the club's official website as he watched training on Monday, and confirmed there were irons in the fire.
"There's certain things happening behind the scenes and there's probably one, two, maybe three people that could be joining Rotherham," he said. "The talks are going well and hopefully one, two will be out here this week."