The pair were instrumental in Liverpool's success last season as Rafa Benitez's side proved credible challengers to Manchester United in the Premier League title race.
Reds captain Gerrard, who is currently injured and misses Wednesday night's crunch UEFA Champions League clash with Lyon, played some of the best football of his career alongside the Spaniard.
Alonso moved to Real Madrid in the summer and many have credited his departure as being a significant factor behind Liverpool's dramatic slump in form.
Gerrard knew it would take Liverpool time to adapt to life without Alonso, who
in a playmaker role was a vital cog in Benitez's team.
"Devastated, yeah. Devastated. But there was nothing I could do about it," he told FourFourTwo magazine.
"Xabi said a long time ago that he wanted another chapter in his career and finally he got it and his team-mates and the coaches couldn't stand in his way.
"We just have to say thanks and move forward without him.
"It's always going to be different when you lose one of the best players in the world - and people are finally realising that's what he is, on the back of his form for Real Madrid and the difference in us from last year.
"We've got other midfielders here doing a good job but it will take a while before Alonso's out of our system because he was such a top player."
Liverpool recouped around £30million for 27-year-old Alonso, and spent most of that on bringing replacement Alberto Aquilani to Anfield from Roma.
Aquilani missed the first two months of the season due to injury and Liverpool have already lost seven matches.