Jasper Cillessen
Jasper Cillessen suffered a muscular injury during the Christmas break. Getty

Barcelona's back-up goalkeeper Jasper Cillessen has given Luis Enrique a much-needed boost by returning to training ahead of the second leg of the Copa del Rey last 16 match against Athletic Club Bilbao on Wednesday night (11 January). The Spanish boss thus has a full squad available for the crucial encounter as the La Liga giants host the Basque side in search for a victory following the 2-1 defeat suffered last week at San Mames.

Cillessen arrived at the Nou Camp during the summer transfer window as a replacement for Claudio Bravo, and was the first-choice keeper in the previous round of the Copa del Rey against Hercules.

However, Marc-Andre ter Stegen had to play in the last week's defeat at Bilbao after the former Ajax keeper returned from his Christmas holidays with a muscular injury.

The 27-year-old stopper also failed to make Luis Enrique's squad for the weekend's 1-1 draw against Villarreal, amid reports suggesting he could be on the sidelines for two weeks.

But Barcelona have now revealed the Dutchman was back in training on Monday morning alongside the rest of his teammates as the Catalans begin the preparations for the crucial encounter with Ernesto Valverde's men.

"It was back to work on a blustery Monday morning at the Ciutat Esportiva, where the players that featured in the previous night's exertions went through the typical warm-down routine and the rest of the squad trained as normal. It was great to see Jasper Cillessen back on the field. The goalkeeper picked up a soleus injury over the Christmas break but is now well on the mend," Barcelona confirmed on their official website. Nevertheless, it is still uncertain whether he will be 100% fit to play on Wednesday or if Luis Enrique opts to keep Ter Stegen between the sticks instead.

Lionel Messi, Andres Iniesta, Luis Suarez and Gerard Pique also took part in the workout after the club opted to not send them to the Best FIFA Awards Gala due to the importance of the Wednesday's encounter. Barcelona are yet to win a game in 2017 and anything other than a win in this game will see them wave goodbye to their chances of retaining the cup.