Sakho did not travel to Morocco to represent Senegal this month, despite his call-up, after claiming he was injured and unfit to play.
However, the powerful forward has gone on to play for West Ham in recent weeks, leaving the Senegal national team so angry about the issue that they have lodged an official complaint to FIFA.
There have been many accusations directed towards the Hammers, but Sullivan insists that Sakho did not go because of medical advice and that his injury was a genuine one.
"A top back surgeon said Sakho can’t fly and he still can’t fly, he went by car to Bristol and is going by train to Liverpool,' Sullivan said. "How can we go against medical advice?
"We are sure any FIFA hearing will vindicate us. The player missed four games as a result of injuries incurred whilst playing for Senegal. We have done nothing untoward."
Senegal had to endure a disappointing African Cup of Nations campaign, with the side exiting at the group stage thanks to a defeat in their final game against Algeria.
Without their main striker, Sakho, they lacked a cutting edge and his presence was definitely missed.
While back with West Ham, Sakho has been in good form, despite his apparently troublesome back.
The striker came off the bench to net the winner against Bristol City in the FA Cup, taking his tally to 10 goals for the season.