Middlesbrough and Ipswich Town join Leeds United in race for Nottingham Forest midfielder
He has previously reported that Leeds want the Forest man in their ranks.
O’Brien was one of the Championship’s most admired midfielders during his Huddersfield Town days, although his move to the Premier League has not worked out.
He found himself out of favour at Forest last season, spending time on loan at D.C United after a proposed move to Blackburn Rovers fell through.
Forest are said to be fielding loan enquiries but have not yet found a potential buyer.
O’Brien has been linked with Leeds on numerous occasions in recent years, with former Whites boss Marcelo Bielsa reportedly an admirer.