The 22-year-old Scotland international striker will remain at the Gers until the end of the season.
The youngster moved to Forest from Scottish club Hibernian in the summer of 2017 for a transfer fee reported by The Nottingham Post to be worth £1 million.
Cummings was signed by then Forest manager Warburton, and the striker failed to make a huge impact at the City Ground, scoring just one goal in 14 Championship starts before joining Rangers on loan.
Warburton told The Scottish Sun: “I read some articles that Jason failed down south. Utter nonsense. He’s just a young player who was adjusting to the demands of a different league.
“With the greatest of respect, the English Championship is a more demanding league than Scotland’s top flight, with far bigger, tougher defenders.
“I never doubted Jason would score goals in England. But now he’s back in Scotland with Rangers and I wish the boy every success.”
Mark Warburton is right
True, Cummings did not make a huge impact at Forest in the first half of the season, but the Scottish striker was at the Reds for only a few months.
It takes time for a player to adapt to the rigours of the Championship, and if the 22-year-old returns to the City Ground in the summer of 2018, then he could well become an important player in Aitor Karanka’s team.
What must also be noted is that Cummings is only 22 years of age and is still developing as a footballer.