Rovers have brought in eight new faces this summer as they prepare for a shot at promotion from League Two next term and currently have 26 players on their books.
Forwards Joe Dodoo and Jordy Hiwula left the club last month – and more exits could follow.
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"There comes a point where the line is drawn," said McSheffrey, whose side get their campaign under way against much-fancied Bradford City on Saturday.
“You might even have to move one or two out.”
The likes of defender Bobby Faulkner could be allowed to leave the club on loan in the near future to gain first-team experience.
Centre-back Faulkner, aged 17, signed a new two-year contract with Rovers this summer and has featured throughout pre-season.
A loan move to a National League North club last season was scuppered by an ankle injury.
Club bosses believe he is capable of competing at that level this term and Adam Long’s arrival could pave the way for a temporary switch.
Other fringe players could also be allowed to leave to balance the books and free up more funds.
Jack Degruchy, an 18-year-old attacking midfielder formerly of York City, featured in Saturday’s 3-0 win over FC United of Manchester as a trialist.
Also involved was striker Tavonga Kuleya, who is bidding to win a professional contract with Rovers after recovering from injury. And Rossington Main midfielder Bailey Conway has spent pre-season at Cantley Park.
On the remaining trialists, McSheffrey said: “They wouldn’t be in the building if they didn’t have an opportunity to stay here.
"There is a line that’s got to be drawn on numbers and figures.”
Meanwhile, Doncaster had sold 1,700 tickets for the trip to Valley Parade as of Monday.
Hosts Bradford will, as always, be well-backed.
The Bantams averaged more than 15,000 fans at home games last season – the highest in the fourth tier.
As of last month the club had sold in excess of 14,000 season tickets amid a wave of optimism under former Manchester City boss Mark Hughes, who has made a number of eye-catching signings ahead of his first full season in charge.