Jurgen Klopp and Pep Guardiola have expressed their bemusement at how Chelsea were able to bring in a number of big-money signings in the January transfer window.
Since the summer transfer window opened, Chelsea have spent more than €600 million on new signings ($650m). The club sealed a record transfer worth €120m ($130m) for World Cup winner Enzo Fernandez from Benfica on deadline day of the January window with seven other players added to the squad throughout the month.
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When asked about the spending of his side's Premier League rivals at a news conference on Friday, Liverpool boss Klopp said: "I say nothing without my lawyer. I don't understand this part of the business but it's a big number.
"They are all really good players so congratulations. I don't understand how it's possible, but it's not for me to explain how it works."
Premier League champions Manchester City are notorious big spenders in the transfer market but made just one signing, Maximo Perrone from Velez Sarsfield, in January despite trailing league leaders Arsenal by five points.
Guardiola said he does not concern himself with Chelsea's spending and prefers to focus on his own side's achievements.
"It's none of my business," he said. "It's a surprise because it's not a club state.
"What I can control is the fact we won 11 titles in the last five years being one of the five or six net spend teams in the league. This is all I'm concerned about what we've done so far in this time."
When asked what the reaction would be if his club spend the same amount, Guardiola replied: "I know what would happen. What Chelsea have done is none of my business. We know what we are working.
"What Chelsea, Arsenal, Liverpool, United, without good players you have to spend. Now the market is 'wow'. What they do is not my business. There are regulations, I don't forget the eight or nine teams that sent a letter to the Premier League to get us banned. We are the fifth team in net spend."
City sit second in the Premier League table and face Tottenham Hotspur on Sunday, while Liverpool visit Wolves on Saturday.
Information from Reuters contributed to this report.