Monaco, who themselves have struggled since the start of last term, have an option to buy in the deal.
“I am very happy to return to AS Monaco, a club with which I hold, of course, fantastic memories,” said the France international midfielder.
Bakayoko came to global prominence at Monaco, where in the 2016-2017 season he was crucial as Leonardo Jardim’s side won the Ligue 1 title and reached the semi-finals of the Champions League playing alongside Fabinho, now of Liverpool, and Manchester City’s Bernardo Silva in midfield.
He was sold to Chelsea the following season but failed to impress during his time in England and was loaned to AC Milan after just a year in London.
However that move also failed to work out, with Bakayoko playing 42 times in all competitions but falling out with coach Gennaro Gattuso as the seven-time European champions finished fifth and missed out on Champions League football.
