The 27-year-old frontman, who has netted 30 times for the Reds this season, picked up the award on Sunday evening.
"He's had an absolutely fantastic season," Rush told BBC Radio 5 Live.
"Last season Gareth Bale and Luis Suarez were the best players. Obviously Bale won it but I think Suarez has surpassed what he did last year.
"He's been fantastic. He's not just a great goal scorer - it's his work rate as well."