Potential signings, including a possible return for former England midfielder Tom Huddlestone, will have to wait.
Having borrowed money from the Football League to help them through the Covid-19 pandemic, the Tigers are under a transfer embargo until it is paid back.
The only signings they can make must be free or loans, and only then to top their squad up to 25 senior players. The arrivals of Nathan Baxter, Randell Williams, Andy Cannon, George Moncur and Ryan Longman have got them to that mark but Hull were under the impression they had two slots available after loaning out Callum Jones and Jordan Flores.
They have asked the League to reconsider, with coach McCann saying he would not have loaned either out had he known.
The Tigers would like to loan Regan Slater from Sheffield United again but the midfielder has been training with the Blades in pre-season. Two divisions apart in 2020-21, they are now Championship rivals.
Hull are also interested in Terell Thomas to provide competition at centre-back where Reece Burke and Jordy de Wijs (who spent the second half of last season on loan at Queens Park Rangers) have moved on. Thomas was released by Wimbledon.
Huddlestone, also a free agent, played the first half of Saturday’s friendly at Scunthorpe United and has left the door open to return to the club he left in 2017.
“We still need another three players in my opinion,” said McCann.
“We need to add to the midfield so hopefully there will be two bodies coming in there and a right-sided centre-half.”
Hull will have to sell players or make Jones or Flores’s exits permanent to bring anyone in before the August 31 transfer deadline.
Flores, who has made only four substitute appearances since joining in January, is out of contract when his season-long loan at Northampton Town expires.