The 31-year-old is currently recovering from the stress fracture he suffered in the win over Tottenham on April 4.
Rovers are desperate for numbers up front in their battle against Premier League relegation, with Roberts joining want-away strike partner Roque Santa Cruz on the sidelines.
But the forward does not expect to be ready for Saturday's meeting with Wigan Athletic at Ewood Park and has hinted that he could remain sidelined for the following weekend's trip to Manchester City.
"The injury is a strange one because if you have a broken bone then you know exactly how long you are going to be out for," said Roberts.
"However, with a stress fracture you can't be sure as it is not as straightforward so you have to be careful in case it happens again and you have a setback. It is doubtful I will be ready for next week."
Roberts, though, is confident one-time Premier League champions Blackburn will avoid dropping into the Championship.
Rovers lost to fellow strugglers Stoke last weekend but Roberts believes boss Sam Allardyce, who replaced Paul Ince in December, has the club pointing in the right direction.
"Under the new manager - Sam Allardyce - our record is good as, apart from Saturday, we have only lost against the top four," he added.
"If we carried on like that over the course of a season then I don't think we will have too many issues over staying up. It is a very tough league but if we remain focused then we will be alright."
Blackburn 10/11, Draw 12/5, Wigan 16/5