Boss Gary McSheffrey was hopeful the new addition would be cleared to train with Rovers today and be able to feature at Cambridge.
Paperwork on the deal was not completed this morning but there were not any issues forecast.
The Free Press understands the player in question is an attacker who will join on loan from a Premier League club.
McSheffrey said: “We can expect one today, we’ve got a player in the building.
"We’re just going through the final paperwork etc so hopefully that will be logged and registered today and we can make an announcement.
"Hopefully he’ll train and it’ll go through in time. If he is registered he’ll definitely feature on Tuesday.”