He scored the opener and then set up the second and third as Arsenal went 4-0 ahead inside 22 minutes at the Emirates Stadium.
But Monreal then looked to be struggling after a knock around the half-hour mark and was swiftly withdrawn, per Arsenal's Twitter account:
Arsenal FC @Arsenal
Let's try that again... We've been forced into our first change - well played, Nacho 👏 🔛 @Ains_7 ↩️ @_nachomonreal #AFCvCPFC 🔴 4-0 ⚫️ (34) https://t.co/OFGQcPbgsE2018-1-20 15:37:04
The 31-year-old Spaniard is one of manager Arsene Wenger's top depth options along the back four, capable of playing both as a full-back or in the heart of the defence. Monreal may not be an automatic starter, but he's the type of versatile option any team would love to have on the books.
Wenger demonstrated his tactical versatility in the 2016-17 season, and Monreal played a big role in that, as he was able to slide forward and feature in the 3-4-2-1 formation the team used toward the end of the campaign.
While he's not the flashiest full-back, Monreal is a dependable option who can defend and attack. He's not a great crosser, but he makes up for it with tremendous range and a work rate younger players should observe.
Losing Monreal hurts, although the Gunners have depth at left-back and should be fine moving forward.