Injury has ruled out loan striker Tony Watt for the remainder of the campaign.
The Scottish international pulled up within five minutes of the Ewood Park clash against Preston North End last Saturday, immediately signalling that he would need to come off.
The forward underwent a scan after the weekend, with the groin injury serious enough to cut his loan move with Rovers and his season short.
"Tony is on his way back to Charlton, that is his season over," Lambert told Rovers PlayerHD. "He's gone to see the doctors down in London it is going to be a few months.
"He was excellent for us on and off the pitch, a good guy, a talented player and obviously we've lost him at a time when we've needed him around.
"We thank him for his efforts coming here and he's got to go back down to Charlton."