'DWTS' Celeb Janel Parrish -- 'Pretty Little Liars' Could Sabotage Dance Title

Janel Parrish is pulling double duty on "Pretty Little Liars" AND "Dancing with the Stars" -- and TMZ has learned she's spread herself so thin, she's alienated castmates on both shows.

DWTS sources tell us ... Janel's pro dance partner, Val Chmerkovskiy is freaking out ... because she's missed two days of critical dance rehearsals due to long days of filming on PLL.

We're told ... Val believes he and Janel have a real shot at winning the trophy -- the finals are Monday and Tuesday -- but thinks her PLL schedule is sabotaging their chances.

As for Janel's "Pretty Little Liars" co-stars ... we're told Lucy Hale and others in the cast have been conspicuously absent from the DWTS set the entire season ... and have given her little to no support -- even when she danced to the PLL theme song.