Five players - Marc-Andre ter Stegen, Claudio Bravo, Ivan Rakitic, Luis Suarez and Jeremy Mathieu - have already arrived at Camp Nou for a combined cost of around €156 million (£124m).
And Bartomeu has now revealed that new boss Luis Enrique may well add several more new faces to his squad before the September 1 deadline.
He told reporters: "The transfer window isn't over yet, it ends in a months' time. I think we still have some things left to do this summer."
Reports in Spain have suggested that Camp Nou sporting director Zubizarreta and coach Luis Enrique will be meeting on Friday to finalise transfer plans, with young Paris Saint-Germain centre-back Marquinhos seen as their first-choice option.
Barca are desperate to do as much business as possible this summer with a potential 14-month transfer ban looming for breaking rules involving the international transfers of players under the age of 18.
The club were initially banned from buying any players for that period starting from April, but Fifa agreed to put that suspension on hold after the Blaugrana lodged an appeal.