If Assombalonga recovers from a hamstring strain, the City Ground is set to host a mouthwatering face-off between two strikers averaging more than a goal a game in recent weeks.
The pair, who both made their name at Peterborough United, have found the net 19 times between them in the Championship this season – in just 22 appearances.
Gayle, the division’s top scorer, missed numerous chances as Newcastle agonisingly crashed out of the EFL Cup on Tuesday night.
But the former Crystal Palace striker was badly missed in Saturday’s shock league defeat against Blackburn, and so is expected to play against Forest.
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Assombalonga has also been sidelined, but he is rated by many as the only striker to compare with Gayle outside the English top flight, and will start tonight, if fit.
But who has the edge? Here’s how the two men match up in the Championship in 2016-17.
Goals/Minutes per goal
Gayle: 13 goals. 85 minutes per goal
Assombalonga: 6 goals. 66 minutes per goal.
Gayle’s tally of 13 league goals has him two ahead of nearest rivals Glenn Murray and Scott Hogan for the Championship’s Golden Boot.
Nine strikes in his last six starts have helped keep him ahead of Aleksandar Mitrovic in the United pecking order.
But Gayle’s record of one goal every 85 minutes this season is eclipsed by Assombalonga’s six goals in 395 minutes – a ratio of one every 66 minutes.
Due to his injury struggles, the DR Congo forward has only made eight appearances, meaning he is averaging a goal every 0.75 games.
Assombalonga’s injuries have had a major impact on Forest this season and had he appeared more than eight times, they would no doubt be higher than 17th.
Shots per game/Shot accuracy
Gayle: 60% shot accuracy 3.6 shots per game
Assombalonga: 80% shot accuracy 1.25 shots per game
Assombalonga’s stats are affected by the fact he has played less than half an hour in four games this season.
Gayle has taken 43 shots in total – incredibly, 12 of those came in the 4-3 win over Norwich – and hit the target with 26 of them.
But Assombalonga’s accuracy is even more impressive, having hit eight of 10 shots on target.
Price/Price per goal
Although £10 million Gayle was one of the most expensive signings in Championship history, he has gone a long way towards repaying that investment by scoring the goals to take Newcastle top of the league.
Having hit the net 13 times, his current price tag is £0.76m per goal, but his lasting value to Newcastle could be incalculable if he fires them to promotion.
Assombalonga’s 23 goals for Peterborough in 2013-14 prompted then Forest boss Stuart Pearce to spend £5.5 million on him at the end of that season.
The Congo DR international has since scored 22 times for Forest, meaning each goal has cost owner Fawaz Al-Hasawi £239,000.
In terms of shooting accuracy and price per goal, Assombalonga may appear to more than match Gayle.
But the simple fact he has been on the pitch far more often than Assombalonga, earning him a much better overall goal tally, means Gayle has the edge.
Assombalonga has also taken less pitch time to score his goals, but Gayle is no slouch in that regard, and to average a goal less than every 90 minutes across far more games is also in his favour.
The importance of Gayle’s goals also cannot be overlooked.