Wigan pleased with Nicholls progress at Northampton
Martinez admits it was a no-brainer to sanction the deal after seeing an "immense" improvement in Nicholls, both on and off the field, during his time at Sixfields.
"We've been very pleased with Lee's development at Northampton and it was an easy decision to allow him to stay down there," Martinez told the Wigan Evening Post.
"He has adapted to first-team football magnificently, and it's important we allow him to continue to develop as a player and a person. We still have a 24-hour recall option should we have any injuries here but he will be there until the end of the season."