The Saints had a £12m bid accepted by the Scottish side last month, but they were unable to agree terms with the Kenya international.
The Premier League club have now come back in for the 22-year-old and are prepared to increase their initial offer in a bid to fend off interest from newly-promoted Cardiff City.
"Southampton have showed an interest again but the bid is there," Lennon told reporters.
"It's the negotiations between Southampton and the agent I'd imagine that might get the thing rolling again.
"I had a chat with him the other day. He is a wee bit confused about things but what we gather is that Southampton have reignited their interest."
Wanyama joined the Bhoys from Belgian side Beerschot in 2011.