Atlético did not say exactly how long Morata is expected to be sidelined. It hosts Liverpool on Feb. 18 in the first leg of the competition's round of 16. The second leg will be on March 3 in England.
Atlético coach Diego Simeone also can't count on forwards Diego Costa and João Félix because of injuries. The club unsuccessfully tried to sign Paris Saint-Germain striker Edinson Cavani in last month's transfer window.
Saturday's loss to the city rival at Santiago Bernabéu Stadium left Atlético in sixth place in the Spanish league, 13 points off the lead after 22 matches. Its next league match is on Saturday at home against Granada.
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