Goalkeeper Emi Martinez, who missed Wednesday's 4-1 loss at Manchester City due to illness, has also returned to the squad, Emery added.
"Jacob Ramsey is again with some problems in his toe, he is not going to be available for the rest of the season," the Spaniard told reporters.
"Emi and Ollie are included in the squad for tomorrow ... we will prepare for the match in the final 24 hours and tomorrow we will know if they’re available and ready to play."
Watkins, who missed the trip to City with a hamstring injury, is Villa's leading scorer in the league with 16 goals.
Villa are fourth with 59 points from 31 matches, two points ahead of Tottenham Hotspur who have a game in hand.
"We are doing the plan we prepared when I arrived here. It was to be demanding in our way," Emery added.
"To include us in the teams that are now contenders to be in the top seven positions in the table is very difficult. We can achieve it like we are doing now, but to be consistent for a long time is the difficulty.
"That is my objective. We are trying to be a contender more than we were before," he said.
Brentford are 15th on 28 points, six points above the relegation zone.
