Blashill told reporters at the Stars & Stripes Showdown on Sunday that he doesn't expect Zetterberg to play the upcoming season if he is not cleared by the Oct. 4 regular-season opener.
"I know it's been a hard summer for him. I know he hasn't really been able to train," Blashill said. "He gutted it out for two months at the end of the year, and it was amazing to see. But it's one thing to gut it out for two months; it's another thing when you haven't been able to train at all to be able to play an NHL season. I know it's been a real hard summer, and I know ... there's lots of doubt to where he'll be at."
Zetterberg, 37, has been dealing with a lingering back issue but is holding out hope that he'll return to play.
"I will need more answers from doctors before I say I have played my last game," Zetterberg told the Detroit Free Press on Tuesday. "In my mind, I am hoping it can get solved.
"I don't want to think I have played my last game. To me, it's still early to say that. But obviously, I've been through this for the last few years, and I know it's a thin line."
Blashill said Sunday the Red Wings would have a better idea of Zetterberg's status as training camp begins Sept. 14. Blashill indicated that Zetterberg told him he hasn't been able to train, giving Blashill doubt that the winger could make it through a full season.
"If he comes into camp and is in a spot where he's not cleared, I wouldn't plan on him for the rest of the year," Blashill said. "That would be my take, because I don't know how you go from not being able to train and then not cleared to all of a sudden being cleared."
Zetterberg had played in all 82 games over each of the past three seasons. He had 11 goals and 45 assists in 2017-18 as the Red Wings missed the playoffs for the second straight year.
"Every time I try to amp up my workouts, I get symptoms again," Zetterberg said Tuesday. "Surgery is not an option. Since February, it has slowly gotten worse -- things like nerve pain down your legs, disk-related issues. I was able to find a way to get through it, but it has slowly gotten worse.
"I need someone to tell me I can't play hockey anymore."
The two-time All-Star took home the Conn Smythe Trophy in 2008 as Detroit won the Stanley Cup. In 2015, he was honored with the King Clancy Memorial Trophy, which recognizes a player's leadership and humanitarian efforts.