Exclusive: 'Dancing With the Stars' pro Maksim Chmerkovskiy sidelined with calf injury

— -- "Dancing With the Stars" pro Maksim Chmerkovskiy will be sitting out tonight's show because of an injury, ABC News has learned.

The season 18 "DWTS" champion sustained a calf injury during rehearsals on Friday with Heather Morris, a former backup dancer for Beyonce and a star on "Glee."

Troupe dancer Alan Bersten will take Chmerkovskiy's place with Morris, but Chmerkovskiy will be in the ballroom cheering her on.

Chmerkovskiy's return to the stage is unknown, but he is getting treatment for his injury.

"Dancing With the Stars" airs Monday at 8 p.m. ET on ABC.