But the German said the vice-captain, who has been sidelined with a muscle issue, could return for the season's final game against Chelsea on July 22.
"My last information is from yesterday because today I didn't speak to anybody because we have training later," the manager told his pre-match press conference.
"Millie is in contention, or is pretty safe for the Chelsea game; nobody told me yet he will be available for tomorrow – and he didn't train yesterday, so that's not a good sign then.
"But it will be fine for Chelsea, I am pretty sure.
"Apart from that, no new injuries on the list, so we should have the same squad like we had for the Burnley game."