The 18-year-old has progressed through Forest’s academy and regularly trained with the first team without making a senior appearance for the Premier League club.
He was named in Forest’s squad for their Europa League meeting with Porto last season and has also played for the club’s under-21 side.
The teenager joins Truro after Dominic Johnson-Fisher left the club for National League side Worthing last week.
Truro manager John Askey believes Blake can provide an attacking threat during his spell in Cornwall.
“Zyan has a lot of ability and can go past a player,” Askey told the club website.
“He is quick, has a good shot on him, and has scored goals at youth and under-21 level.
“He can be a good impact player for us and if he does well, he will be looking to start games.”
Blake is permitted to play in Truro’s FA Cup third qualifying round tie against Cirencester Town if selected.
Askey also sees the move as evidence of the progress being made by the National League South club and believes Forest’s decision to send Blake to Truro reflects the environment available to the young forward.
“This signing shows we are moving forward because if a club like Nottingham Forest allows players to come to us, it’s because they know the lad is going to get treated properly.”
Blake will wear the number 11 shirt during his loan spell and will be expected to compete for regular opportunities as Truro look to strengthen their attack.
The move gives Askey another option in the final third and gives Blake the chance to gain senior experience after establishing himself in Forest’s development sides. He will hope to use the spell to push closer to first-team football at his parent club.
Askey believes the move can benefit both the player and the club during a busy part of the season.