The Gunners will have a fight on their hands if they are to land the 22 year old, with both Serie A side Napoli and La Liga table toppers Barcelona also keeping tabs on the Spanish Under 21 international.
Castillejo has had an excellent start to the season in Spain, having scored one goal and contributed four assists in just ten league games this campaign. A muscle injury has curtailed his game time somewhat, with the winger having missed a month of action before returning to the substitute bench for last weekend’s 2-0 defeat to Barcelona.
Since arriving from Malaga for €8m in 2015, the Spaniard has been a regular in Villarreal’s first team with over 100 appearances for the Yellow Submarine, but it has only been this campaign where his potential has begun to be realised. It is likely that Arsenal will continue to monitor Castillejo to see whether the improvement in his game is sustained over a longer period of time.