Nikolay Nikolaev started playing football at PFC Levski Sofia’s academy. Between 2016 and 2018 he competed for OFC Spartak Pleven and FC Hebar Pazardzhik. He was also in FC Dobrudzha Dobrich when the team performed in Bulgarian second tier.
Nikolaev joined the main squad of Lokomotiv Plovdiv in August 2019. That was the beginning of a great season (2019/20) for him and the club as Loko triumphed with both the Bulgarian Cup and the Bulgarian Supercup trophies.