The creative midfielder was frustrated with the Donetsk outfit's loss at Stamford Bridge, but remains hopeful the Ukrainian side can reach the next round.
The Ukrainian champions appeared to be on their way to a 2-2 draw until Victor Moses helped the hosts to the full three points with a stoppage-time goal, much to the frustration of the star Brazilian, who scored both of Shakhtar's goals to bring the club out of one-goal deficits on both occasions.
"We are very sad. We know that our performance was quite good and we didn't deserve this defeat, especially the way it was, conceding a goal in the last minute," the Brazilian told reporters. "So we are really sad, but hopefully in the next match we will win again."
The attacking midfielder then went on to discuss his side's chances of making it to the knockout stage and stressed that Juventus could cause problems in the last group match. Shakhtar faces Danish champions Nordsjaelland on Nov. 20 before finishing out group play at home against Juve on Dec. 5.
"Juventus have a great squad, full of good players," Willian said. "They are still in the game, because they will host Chelsea in next round and certainly they will do their best to win. But it's all in our hands. We must win away [against Norsjaelland]. We know it's hard, but our qualification will be decided at home against Juventus if we do it."