Two Reasons Why Aubameyang can't play for Arsenal vs CSKA Moscow in the Europa League

Why can't Pierre-Emerick Aubameyang play in the Europa League?Unlike Barcelona's Philippe Coutinho in the Champions League, Aubameyang is not cup-tied for the Europa League.

The Arsenal striker did represent fellow contenders Dortmund in European football earlier this season, but only in the Champions League.

The reason Aubameyang is ineligible to play for Arsenal is because only one player could be registered for European football in January.

As Henrikh Mkhitaryan signed for Arsenal first, he was added to the Europa League squad, leaving no room for former Dortmund team-mate Aubameyang.

What are the rules in a nutshell?

The main rules surrounding eligibility of new signings are as follows:

• No player can play for two clubs in the same European competition in one season.
• Only one new player can be registered for a European squad during the January transfer window.