The Football League fell in line with the Premier League and other competitions around Europe in 2016 by scrapping emergency loans outside the summer and January windows.
Before then, clubs had been allowed to sign players on temporary deals ranging from 28 to 93 days.
Bradford have fallen foul of the restrictions this season thanks to an injury crisis that has been compounded at times by key players picking up suspensions.
Ideally, Hopkin, appointed in September after the summer window had closed, would have been able to bring in a couple of experienced loanees.
But, instead, the Scot has had to play several players out of position, while also scouring the free agent market.
“It is different if you are a Championship or Premier League club because you should have a big enough squad to cope,” said Hopkin. “You should have good enough younger players to fill a bench.
“But I think the loan window should be open all the time for League One and League Two.
“You might get five or six players at every club in the Championship who aren’t playing. It gives them an opportunity to go and play. Same with younger players.
“It would make League One a bit more competitive. Most clubs might not use it because they have got a strong enough squad.
“But if you have got injuries in certain key areas – like where we are just now – you are trying to shoe-horn in people and ask them to do a job that they’ve probably never played in their life.”
Bradford’s season is not about to get any easier with Portsmouth’s visit tomorrow meaning Valley Parade will host a bottom versus top encounter.
George Miller and Ryan McGowan will return from suspension after missing the 4-0 defeat at Gillingham, while Adam Chicksen is back after missing the last dozen games through injury.
Hopkin, though, is still keen to strengthen his squad with former Blackburn Rovers utility man Paul Caddis – a free agent – having trained with the Bantams this week.