Former major league pitcher Dirk Hayhurst, now a broadcast analyst for the Blue Jays, told Toronto radio station Sportsnet 590 The Fan on Thursday that Buchholz was "absolutely" cheating in Wednesday's start.
An article on the Sportsnet website included photographs of Buchholz, including one showing him wiping his first two fingers across his forearm, which appeared to be partially covered with a white substance.
Buchholz brushed aside the allegations, saying he puts rosin on his arm and occasionally wets his fingers to get a better grip.
Farrell insisted the photos were "false" and backed Buchholz's claim about rosin.
Buchholz (6-0) leads the majors in wins and the AL in ERA (1.01).