Brentford say Scott Hogan is recovering well from the cruciate ligament injury he suffered in August.
But Brentford's head of medical Neil Greig told the club website Hogan is "very much on track" with his recovery.
Hogan will now visit knee specialist Bill Knowles in the United States.
"Following this, we hope that Scott will be in a position to begin working outside as a part of his next progression," Greig added.
"No dates are presently being set for Scott's return, as we are working towards key, objective strength and performance criteria, rather than allowing timescales to govern progress.
"This way we can be confident that Scott has achieved the necessary key aims in order to progress back to full function.
"The condition of the knee is testament to the hard work that Scott has undertaken in the past 12 weeks."