The 33-year-old striker has been training with Rovers this summer following his release by Cardiff and is holding out for a permanent contract.
"The situation with Robbie is still up in the air, so he won't be involved against Grimsby," said Blackburn boss Paul Ince.
"These things do take time, especially when the agent gets involved.
"I'm not unsure about Robbie, I'm just unsure as to when it will get done.
"There is no deadline, though, because he is a free agent and not tied down to the transfer window."