A £2.65m transfer fee secured the services of Earnshaw from Derby County this summer and the former Cardiff man will line up at the Liberty this weekend after scoring twice against Morecambe on Wednesday night.
And the threat of the Welsh international is not lost on Martinez who told BBC Sport "If you look at the amount of money that's accumulated in transfer fees, it speaks volumes of the career he's had
"He's got fantastic mobility, he is very clever and he's a goalscorer.
"We have to make sure we are up for the challenge.
"Nottingham Forest paid £2.65m and it shows he should be one of the main players in this division."
Forest followed the Swans into the Championship last season as runners up to the League One champions albeit ten points behind Martinez' men and he added "They really get the ball down and play
"I expect it to be a fantastic advert for Championship football and a game that should be really open and full of good football.
"The two ideas of football were completely different last campaign but I think it is the same now.
"The pressure (of Forest winning promotion) is off their shoulders now and they will come down here thinking they can win."
This article first appeared on JACKARMY.net.