Fredi Kanoute admitted Sevilla's lead was not decisive following the 2-1 victory over Tottenham on Thursday.
Sevilla fell behind to Robbie Keane's opener after just one minute but rallied well to claim an advantage ahead of next week's return leg at White Hart Lane.
Kanoute scored the equaliser against his former club when a controversial penalty was awarded against Paul Robinson after 19 minutes.
The penalty decision sparked ugly scenes in the crowd as trouble broke out between police and Tottenham supporters, before Alexander Kerzhakov headed home for Sevilla after 36 minutes.
"I don't think this is enough for us to be sure of getting through," Kanoute told Spanish television station Antena 3.
"I think we needed another goal, but it is a good result considering they scored first."
Sevilla are the reigning Uefa Cup holders but Kanoute admits it will be difficult to progress past Tottenham and reach the semi-finals.
"I think it is going to be more difficult for us to win it than last year," he explained.
"Tottenham are a very good team and they showed that today.
"We are going to have to fight very hard to get through."