Ballesteros hit the crossbar with a header early on and felt that had the chance gone in it would have set Levante up well to win the game.
"It was a shame that my header hit the crossbar," UEFA.com quotes him as saying. "To take the lead in this game shortly after the start against a team like Rubin would have been good.
"It was a game in which they dominated a little in midfield, but they didn't create problems for us. I think the best chances were ours, except for their last two openings when they pounced on our mistakes. We were looking to win.
"The target in the second leg is to score a goal and qualify for the next round. We know that we will be up against very tough and powerful opposition; there's no doubt that they are going to make things very difficult for us."
The 37-year-old has played for Levante since 2008.