The Championship leader's best lap of 1m 39.782s, set during the morning session, was almost seven tenths of a second slower than the best time of the day, set by his Yamaha team-mate Jorge Lorenzo.
"It was a difficult practice, especially this afternoon. I think I could have gotten a better position but I decided to use just the harder option and work with just that tyre, because we thought that was the best tyre for the race," Rossi said after FP2 at the Andalucian track.
"Unfortunately the performance is very low and the lap time isn't good enough, so I think that also the soft can be an option too, but it will be difficult.
"With the high temperature in the afternoon the track makes you slide a lot and it's very difficult to control the bike. We had a lot of troubles in acceleration, because we suffer from wheel spin and the bike isn't stable.
"We are not good with the setting yet, so we have to try and improve for tomorrow morning. We have a lot of things to do; a different balance of the bike, different tyres and other options."
Rossi's decision to persist with the hard tyre was perhaps related to the effective way he used them in Argentina last time around, where he hunted down race leader Marc Marquez to win his second race of the season.
The Italian's last three race victories have all come having started eighth on the grid.