Madrid became the first side to retain the Champions League title last season, while they also won La Liga as Cristiano Ronaldo spearheaded the double, but Zinedine Zidane's men have endured a campaign to forget in 2017-18.
While acknowledging the challenge of PSG, Beckham said via Marca: "It is going to be difficult with PSG on top form at the moment.
"This is the moment for Los Blancos as they love this competition. Look at the players that they have like Cristiano.
"It is in these moments that the top players come to the fore and the game is going to be incredible to watch."
Beckham won titles with both Madrid and PSG — who are 11 points clear atop the Ligue 1 standings — during an illustrious career, but the 42-year-old refused to pick a side.
"It is very difficult to choose as I like both clubs and they have a lot of passion," the Englishman added.
"I had four great years at Madrid, I was not so long at PSG but obviously winning the league was great. I love the club, the people and the fans are incredible, and I say the same about Real Madrid."