Real host Ajax after beating them 2-1 in Amsterdam last month in the first leg of their last-16 tie, but Ramos will be suspended after he was booked.
Per AS' Carlos Forjanes, Ten Hag said of Ramos' suspension: "It's a big loss for Madrid. [Luka] Modric and [Toni] Kroos boss the midfield, but Ramos is a linchpin at the heart of the defence, and his absence will be both a physical and mental loss for Madrid. Having said that, they can manage without Ramos."
Ramos was Real's best performer in the first leg as he produced an all-encompassing defensive display, winning duels, breaking up Ajax's attacking play and acting as the team's driving force with his impressive passing from the back.
However, shortly after Marco Asensio had restored Los Blancos' lead with his 87th-minute goal—after Hakim Ziyech had equalised for Ajax following Karim Benzema's opener—Ramos got himself booked for a foul on Kasper Dolberg:
The Spaniard's intent was to only miss the second leg and have a clean slate for the quarter-finals if Real make it there, but that won't be the case.
Ajax's task remains the same, though, as he'd have missed the second leg against them because of his booking.
With Real being knocked out of the Copa del Rey and having their slim title hopes in La Liga extinguished since the first leg, Tuesday's game has taken on added significance, as football journalist Rik Sharma observed:
Ten Hag expects Real to approach the game accordingly: "Despite them being third in La Liga, the Champions [League] is their realistic opportunity now to win a title this season, and I imagine this will be evident in their attitude."
He also anticipates Los Blancos will "go for us and put us under tremendous pressure," but he also believes in his own side.
"We're a good team at creating pressure and our possession levels have improved," he added. "We could improve on our counter-attacking play and am confident that if we retain and dominate possession we can take a step forward."
Madrid may be in the driver's seat thanks to their lead and two away goals, but they've struggled recently with three defeats in their last four matches.
They'll now have to take on a side that have scored 82 goals in just 23 Eredivisie matches this season, without their captain and strongest defender.