Simeone wary of Chelsea strength in depth
The Argentinian led his side to a 1-0 win at Valencia on Sunday - Raul Garcia's strike shortly before half-time opening up a four-point gap over second-placed Barcelona.
Like Atleti, Chelsea are embroiled in a domestic title fight, and they produced an impressive display at Anfield on Sunday to beat Premier League leaders Liverpool 2-0.
Much had been made of the selection dilemma facing Jose Mourinho for that match, with the likes of Petr Cech, John Terry and Eden Hazard all injured, and the Portuguese indeed opted to rotate his options for the Anfield clash.
And, the fact that the London outfit put in such an assured display with an apparently weakened side has only served as a warning to Simeone and his men.
"It is clear Chelsea has a huge team because they won despite making a lot of changes," he said.
"That means we are going to play against a powerful team, something we knew.
"So they will make a lot of problems for us next Wednesday."
The sides enter Wednesday's second leg at Stamford Bridge with the score poised at 0-0, meaning Atleti would progress to a first Champions League final in 40 years with a score draw.