The Scottish Sun say Duffy has been sent back to parent club Brighton & Hove Albion after injury ruled him out of selection for the last two games of the Scottish Premiership campaign.
The 29-year-old was viewed as a marquee signing for the then-reigning Scottish champions due to his vast experience playing in the English Premier League and international football with the Republic of Ireland.
However, he failed to fit into Celtic’s style of play and his season-long loan in Glasgow was marred by underwhelming performances before finally finding himself out of the starting XI for good earlier this year.
It has been widely reported that Celtic paid a fee of around £2 million to loan the centre-back, while his wages took total expenditure on the transaction to over £3 million. In total he made 25 appearances in all competitions.