Trollope told BBC Radio Bristol: "It does look like Luke will be missing the start of the season for sure.
"We're still looking at rehab times and the potential for him coming back or having to stay at West Brom for a longer length of time."
Daniels broke down during the warm-up before Rovers' friendly against his parent club and returned to the Midlands for treatment.
Trollope continued: "We would like him back as soon as possible. I don't think he's going to be out for six months or a year but, at the minute, we're unsure if it's going to be a couple of weeks or a couple of months.
"The season starts next week and we need some quick answers."
Trollope might turn to 21-year-old Mike Green to fill the gap.
He said: "We certainly have other possibilities if the news is bad and we have to look elsewhere, but we will have to move quickly.
"Having said that, Mike Green has done well in the last two games. He's made very few mistakes and given good performances."
Green kept a clean sheet as Rovers drew 0-0 at Cheltenham Town on Wednesday night.
Source: BBC Sport
Source: BBC Sport