Fellaini came off in the 75th minute at St Mary’s, sparking concerns the Belgian might not recover in time for United’s European showpiece against Ajax in Stockholm next week.
United manager Mourinho didn’t reveal the nature of Fellaini’s injury, but he suggested the problem wasn’t too serious.
“Fellani hasn’t got a tear but he’s experienced enough to know he had a feeling. Apart from that nothing. It’s all good,” said Mourinho.
United must beat Ajax to qualify for next season’s Champions League and with nothing to play for in the Premier League, Mourinho was relieved to leave the south-coast without any major casualties.
“We played a good team, a team who tried to win and tried to finish well. I think we did more than ok,” he said.
Mourinho was also impressed by the performance of goalkeeper Sergio Romero, who stood in for David de Gea and saved Manolo Gabbiadini’s first half penalty.
Having played several other fringe players against Southampton, Mourinho said the understudies had given him food for thought as he considers his team for the final.
“I think all of them gave me positive feelings. Sergio had a very good performance, more than very good,” Mourinho said.
“The team wasn’t perfect but individually they gave me good things. They showed me they want to be an option for the final.”