I don't recall ever seeing this mentioned before (apologies if it's already common knowledge), but I was intrigued to discover recently that Forest were close to signing Dixie Dean from Tranmere Rovers in December 1924.
Talks were sufficiently advanced for Tranmere to omit Dean from their side for a drawn FA Cup (5th qualifying round) match against Coventry, in order not to jeopardise a deal by leaving him cup-tied. Negotiations stalled, however, and Tranmere picked Dean for the replay; Forest decided that, due to Dean being cup-tied, they would not attempt to conclude a deal. They moved on, instead, to the wonderfully named Randolph Septimus Galloway, whom they broke their transfer record to sign from Derby.
Forest were relegated to Division 2 at the end of that season as Galloway struggled (he would score eight goals in 39 appearances across three injury-affected seasons). They proceeded to spend 32 consecutive seasons outside of the top flight (including the break for World War II) - they would not return until 1957.
Dean was signed by Everton four months after the collapse of the Forest move (Forest went back in for him at that time, but with several other clubs now circling, the opportunity was gone). Dean went on to score 33 goals for Everton in his first full season and the absurd total of 383 in 433 games overall during his time there.
We might just have made the wrong call on that one! Who knows how different the trajectory of the club may have been if Dean's goals had enabled them to escape relegation that season and to establish themselves as a major top flight side during the next decade.
