The centre-back missed the Championship leaders' last game due to an ankle injury.
The Spaniard missed Boro's draw with MK Dons after sustaining an ankle injury which forced him off during the previous clash against Blackburn, and Karanka confirmed that the centre-back is yet to return to training, and thus, suggested that it is too early to know whether he will feature against Steve Evans' men.
"No he's not training and I don't know [if he'll be able to play against Leeds]," he told Gazette Live.
"He's an important player for us and I don't want to take a risk. I have to know how he is right up until Monday."
There is no doubt that having the 25-year-old available will provide Karanka's men with a huge boost ahead of their trip to Elland Road.
The former Liverpool defender's absence against the Dons was only the second time that he has missed a league fixture this season, suggesting that he can take a lot of the credit for Boro's current position at the top of the Championship.
The club have conceded just 16 goals this term, which is the fewest of any side in the division, so Karanka will certainly be hoping that Ayala manages to prove his fitness in time for the trip to face Leeds.