Arsenal midfielder Santi Cazorla believes ex-Chelsea striker Demba Ba will be the primary threat to his side's hopes in their Champions League play-off game against Besiktas.
Ba was the star signing for Besiktas coach Slaven Bilic this summer having come close to joining Arsenal from Chelsea a year ago.
The Senegal striker has been identified by Cazorla as the main threat to Arsenal's hopes of reaching the group stage for a 17th successive season.
"He is a great footballer," Cazorla told the club's official website ahead of Tuesday's first leg in Istanbul.
"He proved that here in Premier League, playing for Newcastle and Chelsea. He is a great signing for Besiktas.
"We better watch out with him and also with all of their players, but he will be a leader for them and we have to be careful because he has scored a few goals against us. If we don't keep our eyes on him then we will be in trouble."
Arsenal can expect to be greeted by a hostile reception from the home supporters - with the match taking place at the Ataturk stadium due to renovation work at Besiktas' own ground - but Cazorla has urged his team-mates to embrace the challenge.
"This Champions League play-off is crucial for us," he added. "Everyone wants to play in the group stages of this competition.
"It is nice to play in these kind of atmospheres, even though it is always better playing at home than away. Nowadays every player enjoys playing in stadiums with great atmospheres and you always have that in Turkey.
"Turkish football is lived with passion, even more so when it comes to a Champions League play-off. This cannot affect us, though.
"We will go there to play football, thinking about what we have to do and trying to separate ourselves from the atmosphere."