The offer is understood to have been from League One rivals Sunderland, who had earmarked Marquis as an alternative target along with Gillingham's Tom Eaves, having been frustrated in their attempts to sign Wigan's Will Grigg after seeing a number of bids turned down.
Reports have suggested that the bid for Marquis was £1.25m.
The offer was understood to be some way short of Rovers' valuation of the player, with the club not keen on doing any business in any case.
Confirming that the club had received an offer for Marquis at his pre-match press conference on Thursday afternoon, McCann reiterated: "No one is for sale.
"The board rejected a significant seven-figure bid for one of our players, because we’re simply not interested in selling anyone we don’t want to.
“What the owners and I are interested in is getting promotion this season.
"Our focus is on getting into that top six, staying there and building on that to turn us into a Championship club next season.
“We have no need to sell anyone. The players are good enough, the club is financially secure and on a great footing, so our focus is on getting promotion and nothing else.”