Frank Lampard believes John Terry's influence on an improving Aston Villa is clear to see.
Lampard's Chelsea host Villa on Monday, with Dean Smith's side enjoying an excellent season.
Villa are above the Blues on goal difference in seventh, despite having played two games fewer than their next opponents.
They have the second-best defence in the division - their 13 conceded only bettered by Manchester City (12) - and are bolstered by a current run of four successive clean sheets.
Villa's backline will be without the suspended Tyrone Mings against Chelsea, although they kept Crystal Palace at bay despite playing more than half of their 3-0 Boxing Day win when down to 10 men.
Smith's squad have not made a single error leading to a goal conceded this term, set against 10 from their relegation-haunted 2019-20 campaign, and Lampard feels Terry's presence on the Villa coaching staff is reaping rewards.
"I'm sure John has an influence," he said. "In my opinion, he's one of the greatest centre-backs to have played in the Premier League, for England and in the world for a long period of time, with an absolute wealth of knowledge of the game.
"His input will be invaluable to Dean Smith and all the staff. The team are working hard, there's a real big uplift in them.
"I'm sure that's down to a lot of work behind the scenes by John and all the staff there."
Lampard is calling on his own players to dig deep after a dispiriting 3-1 derby loss at Arsenal on Boxing Day.
It was a third defeat in four Premier League outings and the Chelsea boss believes adversity will teach him much about a talented, youthful squad.
"I think you certainly do - I learn about the players and the players learn about themselves," he said.
"Some of them are young and some of them are new to the Premier League. These tough times are things that we'll have to go through
"I don’t think this season was ever going to be plain sailing or winning every week. We got into the position we were in by winning a lot of games.
"Things are pretty easy at that point. When you lose a couple of games, they become a bit tougher."
Lampard added: "The only way out of it is to fight and work hard. That's what I'll be instilling in the players, that idea.
"At the same time, when you look at ourselves in the table, we're still close to the top and I feel there's still a big uplift coming because of the youth in our team and the freshness.
"I expect that, but we have to work for it."