But the Rovers boss remains convinced the striker will indeed commit his future to the club.
Rovers opened negotiations with the 26-goal forward before the end of the season as he prepared to enter the final 12 months of his initial two-year deal.
While it was expected to be a smooth and swift process, Marquis has yet to confirm his intention to remain at the Keepmoat beyond 2018.
Following a superb season, speculation has inevitably linked several clubs with moves for the 25-year-old.
But Ferguson refuses to be fazed by any delay in completing the deal, even if it means waiting until the Rovers squad reports back for pre-season on June 26.
“His agent has been on and he understands the situation,” Ferguson told The Star.
“We’re getting closer I feel. I’ve no real concerns.
“I think John has gone on holiday now and we’ll probably get that done when he’s back.
“It might not even get done until we come back for pre-season.
“I’ve no concerns on it.
“The agent and I both spoke on it and we’re confident it’ll get done.”
Meanwhile, Ferguson is this week awaiting a response from a Premier League centre half who could join Rovers on a permanent deal this summer.
Ferguson’s recruitment drive has gathered pace this week with the signing of an unnamed left back while a loan deal for Sheffield United midfielder Ben Whiteman has also been agreed.
And a left sided centre half could be the next item ticked off the shopping list.
“We’re waiting on a decision from a centre half from the Premier League to take on a permanent,” Ferguson told The Star.