The 27-year-old was replaced by Ruben Loftus-Cheek as Chelsea started their European campaign with an impressive performance.
The Brazil international had given the hosts an early lead before Oscar converted a penalty. Diego Costa and Cesc Fabregas added goals in the second half.
Willian lasted just 23 minutes of Chelsea's Champions League tie against Maccabi Tel Aviv
"The most important thing was to win." Mourinho told BT Sport. "If some players had good individual performances, good for them, if some score a goal that was also important.
"The only negative thing was Willian's injury. Apart from that everything was positive. I have a lot of thinking always. I try to read the game before it starts, and I have a lot of thinking before Arsenal."
Jose says he will only start thinking about team selection for the Arsenal game tomorrow. He says Willian and Pedro are out for sure. #CFC
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