"Robbie has signed his contract. It has been an ongoing situation for the last two or three months now," said the Rovers boss.
"But I'm pleased that he has signed, he's a proven goalscorer. It was not long ago that he was banging in goals at Anfield, so it shows that he can still do it at this level.
"It is a three-month contract and if he does well and does the business then there is no reason why we can't extend that."