From Wiki
MacLean, Maclean, McLean, McClean, McLaine, and McClain is a Gaelic surname (MacGill-Eain in Scottish Gaelic). There are several different origins for the surname McLean/MacLean, however, the clan surname is an Anglicisation of the Scottish Gaelic MacGilleEathain. This was the patronymic form of the personal name meaning "servant of (Saint) John" or the "son of the servant of Saint John"
So - John, or Iain, maybe Euan?