Bunn left Sixfields on transfer deadline day in 2008 but only made his league debut for Rovers this week.
Sampson said: "There is a financial boost for us - but not until he plays 20 Premier League games.
"So hopefully Paul Robinson`s injury will be a serious one!
"But it is good to see him get his chance. He always had great ability as a goalkeeper.
"We thought his size might hold him back at the top level but he came on and by all accounts did very well."
Source: PA
Source: PA