The England international picked up a knee injury in the opening Premiership game of the season which is likely to keep him on the sidelines for more than 12 weeks.
It means the Tigers are entitled to break the salary cap to make a signing, as the rules state that when a player is injured for 12 weeks or more, his club may apply to the Premiership's salary cap manager to recruit a replacement, who is then permitted to remain with the club for the rest of the season.
"We have the potential to use injury dispensation on Manu so we will see what is available," O'Connor revealed.
O'Connor also said long-serving back Matt Smith, 32, is also an option.
"Matt was good at the weekend [against Northampton Saints]," added O'Connor. "He has played there a lot for us, has a lot of experience and he will do a good job for us."