Arsenal legend Paul Merson believes Chelsea striker target Diego Costa could hold the key to success in north London this season.

The Atletico Madrid star has been heavily linked with a move away from La Liga, with both Premier League clubs reportedly chasing the £34million-rated forward.

And, the Sky Sports pundit believes the Brazilian could potentially be crucial to Arsene Wenger this season, as the Gunners chase their first title since 2004.

"Arsenal need a centre-forward and badly. I think Olivier Giroud is a good player and I like him but I'm not just talking about this season but next season and the one after," he wrote in a feature on the website.

"Arsenal are in such a good position at the moment you just don't want to blow it in February or March because you haven't got a centre-forward.

"I'd love to see them get someone like Diego Costa from Atletico Madrid who would cost a lot of money but Arsenal have got enough it. If they got him they'd be a massive, massive side."

Chelsea also have problems up-front this season, with Fernando Torres, Demba Ba and Samuel Eto'o all failing to make the position their own in west London.

And, Merson believes that a forward is the best option for the Blues in the transfer window. But, he thinks another big name might be the right man for Jose Mourinho at Stamford Bridge.

"They have got to go and buy a forward. Will they go for Wayne Rooney again? It was clear that Jose Mourinho wanted Wayne Rooney in the summer and never got him so maybe they will go full monty for him in January? He would be a brilliant signing," he said when discussing the club's potential transfer activity.

Whether Chelsea pursue the England striker once again in the New Year remains to be seen, but it promises to be a hectic January transfer window for both clubs.

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