"I'm hoping [Zetterberg] is good and we'll have to address that probably in September. I want to get to [training] camp and see if Henrik Zetterberg is healthy. He's a real unknown."
Speculation this offseason has cast doubt on Zetterberg's return for a 16th NHL season. Zetterberg, who has played his entire NHL career with the Red Wings, had back surgery in 2014. He missed five games in 2014-15 but has played all 82 games in each of the past three seasons.
"He didn't practice the last two, 2 1/2 months of [last] season, he just played games," Holland said.
Holland told the team website on July 1 that he expected Zetterberg to play this season.
"Obviously his back is going to determine whether he can or he can't," he said. "Do I have a clear green light? I'm expecting him to play. Do I have a clear green light? No, I don't know that I've got a clear green light."
Zetterberg, Detroit's captain, had 56 points (11 goals, 45 assists) last season, second to center Dylan Larkin (63 points). Larkin signed a five-year contract with the Red Wings on Friday.
"I know he's played through a lot of pain in his career and he's done so much for our team and city," Larkin said. "But for our team, he's going to help our team no matter what, if he's playing with one leg or whatever. He's one of the most skilled players I've played with and a great leader. I think he's the best player on our team, so I think it would definitely hurt losing him. But he does have to look after his future."
Zetterberg, who had surgery in 2014 to repair a ruptured disk and was unable to play for Sweden at the Sochi Olympics, said before last season ended that he expected to return, and has not said those plans have changed.
"For me it's going to be the same as I've been doing the last couple of years," he said April 3. "I will go into the offseason and try to have a good summer, work on my health, and hopefully I can come back and be better."
Zetterberg has 960 points (337 goals, 623 assists) in 1,082 NHL games, as well as 120 points (57 goals, 63 assists) in 137 Stanley Cup Playoff games. He won the Conn Smythe Trophy as playoff MVP in 2008, when the Red Wings won the Cup.