Villa became Spain's leading scorer when he netted his 45th and 46th goals for the world and European champions against Czech Republic last month, but last found the net for his club against Real Mallorca on February 26, a barren run of six games.
"You always get a bit worried when you aren't scoring but you have to stay calm," Villa told a news conference on Monday.
"I know it's been a while since I scored, but the only way to put that behind me is to work hard in training and on the pitch," the 29-year-old added.
World Player of the Year Lionel Messi, joint top scorer in this year's edition of Europe's elite club competition with eight goals, did not train as a precaution after an injury scare on duty with Argentina.
Barca need to be careful of complacency after Saturday's 1-0 win at Villarreal and focus fully on the Shakhtar match, Villa said.
"When you come into a game after losing or drawing everyone knows you have to put it behind you and concentrate on the next match, but the same thing holds true if you've just won.
"Now we have to try and play well, win and get a good result for the second leg."
However, influential Brazilian midfielder Fernandinho is back in action after seven months out with a knee problem and played the whole of Shakhtar's 3-1 win away to FC Ilichivets Mariupol on Friday.
"Now I am ready to play all 90 minutes. In fact, the whole team are ready," Fernandinho said.
"It is the most important game for us because we have reached the quarter-finals for the first time," he added. "It would be perfect to score in Barcelona."
