Chelsea are expected to appoint a new manager at the end of the season with interim boss Rafa Benitez unlikely to stay on at Stamford Bridge and Blues owner Roman Abramovich is likely to give his new manager substantial funds to bolster the squad.
Wenger is expecting big moves from Chelsea in the transfer market with the likes of Atletico Madrid striker Radamel Falcao strongly linked with a transfer and the Gunners chief fears how strong their London rivals could become with more additions in the summer
"I'm afraid of what Chelsea can do in the summer," the Frenchman told Eurosport.
"We have to be prepared for them to be one of the biggest movers in terms of investment once the window opens.
"Even though they already have a great base to their squad, notably their young players such as Oscar, Juan Mata, Ramires and Eden Hazard, I think they will be busy during the transfer window.
"We've heard a lot of talk about Atletico Madrid striker Radamel Falcao. Some people say it's already a done deal, but I've heard nothing."
Wenger also admitted Jose Mourinho would be a good choice to return to the Chelsea managerial hot seat even though he feels Benitez has done a good job at Stamford Bridge.
"I think Chelsea currently have a great coach in Rafa Benitez, but if they part ways at the end of season, of course Jose Mourinho would be a good solution for Chelsea," added Wenger.
"Mourinho is one of the best in the world. But I consider Benitez to be doing a good job at Stamford Bridge."