Atletico Madrid are hoping Antoine Griezmann's injury is nothing more than a sprained ankle after the forward was substituted in their 1-0 defeat by Inter Milan in the first leg of their Champions League last-16 tie, manager Diego Simeone said.
Inter Milan stretched their lead at the top of Serie A to 10 points on Friday after cruising past sorry Salernitana 4-0 ahead of their Champions League clash with Atletico Madrid.
"(Atletico) are taller and they took advantage of that," noted Ancelotti.
Defeat snapped Madrid's 21-match unbeaten run.
"These moments can only be experienced here. All of us who played gave our all," said Brahim Diaz.
Antoine Griezmann became Atletico Madrid's all-time standalone top goalscorer with 174 goals after netting against Real Madrid in the Spanish Super Cup semi-final on Wednesday.
Real Madrid defeated Atletico Madrid 5-3 after extra-time in a pulsating battle in Saudi Arabia to reach the Spanish Super Cup final on Wednesday.
Los Blancos take on Diego Simeone's Atletico on Wednesday in Riyadh in the Spanish Super Cup semi-final, again next week in the Copa del Rey last 16, and also in La Liga in early February.
Atletico Madrid progressed with a 3-1 win at third-tier Lugo after Memphis Depay struck twice, while Real Betis were knocked out in a 1-0 defeat by Alaves.