A 36-year-old woman is under police guard in hospital after a man was left fighting for his life following being severely burnt in suspicious circumstances in northern Melbourne on Wednesday morning.

It is believed the 49-year-old man was asleep alone in an upstairs bedroom of the Macleod home when his wife allegedly walked in and poured accelerant onto him before igniting it.

Investigators are yet to confirm the source of the fire.

The MFB and paramedics attended the fire at a home on Wattle Drive in Macleod at 5.40am.