Real Madrid fear one of their key players will be banned by UEFA for the first leg of their Champions League quarter-final against Arsenal, according to reports.

The Spanish giants are due to travel to the Emirates next Tuesday, before hosting Arsenal in the return leg eight days later, but have been left sweating on the availability of four stars.

UEFA announced last week that they have launched an investigation into the behaviour of Kylian Mbappe, Vinicius Jr, Antonio Rudiger and Dani Ceballos in the aftermath of Real's penalty shootout win over Atletico last month.

Mbappe is accused of touching his genitals in a derogatory manner, Vinicius Jr allegedly clashed with Atletico fans during and after the game, while Rudiger is said to have made a throat-slitting gesture. Ceballos is also accused of making an offensive gesture.

UEFA are due to deliver their verdict on the four players on Friday, and Real are fearing the worst with regards to Rudiger's predicament.

As reported by Marca, Rudiger's case is viewed as 'different' because his gesture was considered threatening and was not well received.

He could be hit with a fine or a suspended ban, but Real are concerned that a harsher punishment is also a possibility and that he may have to serve a one-match ban.

It is understood that Real expect Mbappe, Vinicius Jr and Ceballos to be fined, while similar cases in the past indicate that a one-match ban could be handed out, but that it would be suspended for a period of time. It would then only be imposed for a repeat offence. 

Rudiger missing out at the Emirates would be a major blow for Real, who looked shaky without the experienced centre back in their latest outing.

Carlo Ancelotti opted to rest Rudiger for the second leg of Madrid's Copa del Rey semi-final with Real Sociedad on Tuesday, and his team conceded four goals in normal time.

The German international was introduced off the bench at the start of extra time and scored the tie's decisive goal in the 115th minute to seal a 5-4 aggregate win for his side as Real booked their place in the final.

Arsenal also have their own defensive issues heading into next week's match, with Gabriel emerging as a major doubt after going off with a hamstring injury in the Gunners' 2-1 win over Fulham on Tuesday.

Jurrien Timber also hobbled off with a knee complaint late on, while Ben White and Riccardo Calafiori missed out on the matchday squad with their own fitness issues and are facing a race against time to be available for next week.