The 28-year-old Scot has already made nine appearances for Oxford on loan from Plymouth Argyle and will now feature in Saturday's big game at Sixfields in which a healthy travelling support is set to help Northampton achieve a season's best league crowd.
"I'm looking forward to getting my head down now and hopefully scoring some goals and helping the team push for promotion," Maclean told BBC Oxford.
"I'm delighted it's all sorted out, the lads and manager have been excellent and the fans are a different class."