READING boss Jaap Stam admitted Millwall will be "difficult" opponents for a lot of teams this season.
Stam's Reading lost 2-1 to Millwall on Tuesday night after two late George Saville goals.
It was the Lions' third successive win at home to add to victories against Championship big guns Norwich and Leeds.
"From what I heard against Norwich they had a difficult time in the beginning as well. And then they score that one goal and it gives them extra confidence," Stam said.
"In how they play they make it difficult for a lot of teams, but the thing is can they keep it up all season and do well against every team they play here or away?
"They are positive and a very strong side in terms of physicality.
"I'm sure they will make it difficult for a lot of teams."
Reading went ahead through Dave Edwards' 73rd-minute header. George Saville scored an 80th-minute equaliser before he capitalised on a ball that was headed out of Reading's box by firing into the bottom corner from 20 yards.
Stam said: "We knew when we came over here it was not going to be easy, we expected them to play like this. A lot of balls up front, battles in the air and for second balls.
"When they go forward and play these balls into the box it's a threat but they didn't create chances.
"Then you get a corner and you're 1-0 up and hoping that they stick to what they've been doing and maybe even score a second one.
"You know they're going to be even more direct, if that's possible. We had Jon Dadi Bodvarsson ready to come on, he's a strong runner.
"Set-pieces, corner kicks, when they have a little bit of time on the ball and put it in the box we needed to be aware of their physicality. That's their strength, that's what they try to do and they succeeded."
Image: Millwall FC