The timing of his registration with the Griffin Park club means the midfielder will only be permitted to face Sheffield Wednesday in the semi-finals.
He told the club's website,
"There's nothing that can be done about it now - I just joined them a bit too late."
"It is a blow, because it will be a tremendous occasion, but I'll be doing my best to help them get there."
He also spoke today about how much he has enjoyed his loan experience at the Bees,
"I've done well there," said Pratley who has been an ever present since joining in the transfer window.
"I won their Player of the Month award last month and I've just enjoyed having the opportunity to play some first-team football. This is my first loan spell and it's been a real eye-opener for me. It's a lot more competitive than reserve football - you know that there's a lot more on the line for everybody if you lose."
"The football's been a bit different as well - a lot more long ball, not as technical as Fulham. At Brentford it's all about the second balls, making sure you win your headers and your races - there's more focus on the nasty bits of the game if you like."
"Playing regular first-team football in front of crowds of 6000-7000 has been a great experience for me. I think I've learned a lot from it and I think it will do me a lot of good for next season."