"The hotel management is in permanent contact with local hospitals checking on the condition of the wounded who are still hospitalised," the RIU group, which runs the Riu Imperial Marhaba Hotel, said in a statement.
"On a positive note, the number of hospitalised has been decreasing but our thoughts are with the six injured who are still in a serious condition," it added.
A Tunisian student disguised as a tourist pulled out a Kalashnikov rifle hidden in a parasol on Friday and opened fire on tourists on the sand and by a pool at the hotel in Port El Kantaoui, near Sousse south of the capital Tunis.
It was the deadliest attack in Tunisia's recent history.
Tunisian authorities have so far identified 18 of those killed as 14 Britons, a German, a Belgian, a woman from Ireland and another from Portugal.
Britain has said at least 15 of its citizens were confirmed dead and warned that the toll is likely to rise.
A further 39 people were injured, including 25 Britons, in the attack which was claimed by the Islamic State group, which controls large parts of Iraq and Syria.
The Riu Imperial Marhaba Hotel was hosting 565 guests at the moment of the attack.
"Although most guests have decided to return home, we have currently around fifty guests staying in the hotel. They have chosen to complete their vacation in Tunisia as planned," the statement added.
RIU runs 10 hotels in Tunisia, including the Marhaba near the resort town of Sousse.