Manager Tony Mowbray says Rovers must be prepared to play the waiting game in their pursuit of new recruits.
Rovers have brought in two new faces so far this summer - Joe Rothwell from Oxford United and Jacob Davenport from Manchester City.
The Rovers boss insists the club are working hard behind the scenes to further strengthen the squad, but Mowbray says deals are proving more difficult as a result of players' participation in the World Cup.
"It's difficult because the Premier League teams have just come back, because of the World Cup," he said.
"They've generally taken their young players with them, because their international players are not back yet or are still on holiday, so they need to make sure their squads are deep and strong enough to play games.
"So the players that probably will be available to go out on loan are not available at the moment, so we have to be patient and wait."
