The 23-year-old Finland international previously played for AZ Alkmaar and PEC Zwolle before signing for Forest in 2016.
And upon sealing his move, Lam revealed he was unhappy during his time in England, making 21 appearances before seeing his game time limited.
Lam says Forest coach Mark Warburton is to blame for his successful spell, as he didn’t give the player a chance.
He told Voetbal International: “I would not get a real chance from manager Mark Warburton.
“He could not guarantee that I would appear in his plans.
“The Finnish coach also said I had to make enough minutes because he could not continue to select me.
“Finally, Nottingham agreed with this choice.”
He further explained: “In the first half of the year I played almost everything, and good too.
“But trainer Philippe Montanier was fired. He was succeeded by the trainer of the second (Brazil), under him I played a little less, but after that Warburton came.
“He actually chose for English players only, the foreigners fell outside the boat. I did not have a chance anymore. That feels unfair, frustrating.”