Securing progression in the Champions League came at a cost.

On Tuesday, Liverpool secured progression in the UEFA Champions League after overcoming Napoli in their final group-stage game. However, that did not come without a cost.

The Reds hosted the Italians on Matchday 6 knowing that they needed a 1-0 triumph or a win by two clear goals in order to qualify for the next round. And that's exactly what they did, as a sole goal from Mohamed Salah was enough to send them into the knockout stage.

The Anfield crowd celebrated this result, but it didn't take long for the fans to receive worrisome news about that game. This is because two defenders picked up knocks ahead of the festive period.

The first is Joel Matip. The Cameroonian completed 90 minutes in the Anfield tie but was later sent to hospital for a scan after hurting his shoulder. The other is Trent Alexander-Arnold, who came off with a foot injury, with Klopp admitting that it was painful.

On the issue of Matip, the German boss was optimistic. James Milner also came off late in the game, but Klopp played that down as a cramp.

"Nobody told me anything about [Joel's] shoulder, so hopefully that's a good sign," Klopp revealed after the game, as per the Sun.

"Trent got a knock on his foot, we are not sure about what exactly it is. It is painful.

"Millie had cramps - I hope it was only cramp. That was it, I don't know anything else."

While the two aforementioned defenders might not be set for lengthy spells on the sidelines, they will likely be doubts for the Merseyside giant's upcoming game: a home clash with Man United. After the encounter with Mourinho's men, Liverpool will travel to Wolves then host Newcastle before back-to-back clashes with Arsenal and then Man City.

Things are made worse by the fact that Liverpool is already without Joe Gomez for the festive period. The Englishman, who has established a solid partnership with Van Dijk at center-back, has been ruled out for six weeks after suffering a leg fracture.

Should Matip and Alexander-Arnold join him on the sidelines for the coming weeks, Klopp will be left with a crisis at defense. The Premier League's only unbeaten side has just claimed the top spot in the standings but face new hurdles in their title chase.