Filipe Luis was Atleti's best - Clement

Real Madrid assistant coach Paul Clement believes his former club Chelsea have signed Atletico Madrid's best player in Filipe Luis but warned that Diego Costa is "not Didier Drogba yet."

After finishing last season without a trophy, Jose Mourinho has moved to reinforce his Blues squad by bringing in Luis and Costa from Atletico as well as Cesc Fabregas from Barcelona.

Clement believes Brazil international Luis, 28, will be a major asset in the Premier League after helping Atletico to the Spanish league title last season as well as reaching the Champions League final.

"Atletico had an amazing season last year, but Filipe was their best player," Clement, who was a member of Carlo Ancelotti's coaching side at Stamford Bridge, said in The Times. "We [Madrid] played them five times and I watched them on countless other occasions, and he never seemed to make a mistake.

"He's good on the ball, reasonably quick and incredibly tough in the tackle. He's smart and resilient, so should be perfect for the Premier League. How he wasn't playing for Brazil this summer I'll never know."

Mourinho regularly cited his attacking options for Chelsea's problems last season. Clement believes Costa will improve a frontline that had consisted of Samuel Eto'o, Fernando Torres and Demba Ba but feels the Spain international's approach will be less effective than in La Liga.

"Costa's aggression and nastiness is the key, as without that he'd be a fairly average player," Clement said. "I'm not surprised Mourinho has signed him as he's the kind of player who'd die on the pitch for his teammates, but he won't find it as easy to bully defenders in England as he did in Spain. He's not Didier Drogba yet, but he's a big improvement on what Chelsea had."

Chelsea have also brought goalkeeper Thibaut Courtois back to the club after three seasons on loan at Atletico and Mourinho has said he now has a squad capable of winning the Premier League.