Frank Lampard believes if Chelsea tie Antonio Conte down to a new contract it would be their signing of the summer.
Conte has signalled his eagerness to stay next season but an extension to his current deal, which expires in 2019, is yet to be confirmed.
The Italian is one of the most sought-after coaches in Europe after leading Chelsea to the Premier League title in his opening season at Stamford Bridge.
And while the Blues are set to make a number of big-money signings this summer, Lampard, who scored 211 goals in 649 appearances for the club, says Conte would be the best.
"Antonio would be their most important signing - for me he was their man of the season," Lampard said.
"You talk about player of the year, I'm all for giving the players credit but because it was such a dramatic uplift from the year before I think you have to give him huge credit.
"You saw the system change and how he made them play in that formation, it worked well.
"I think he's a huge signing for them. I have no doubts, I don't know but I'm pretty confident he'll be there and they'll bring in players to play in the system he wants to play."
One man who looks likely to leave Chelsea is Diego Costa, with Conte making clear to the Spain international he is no longer in his plans.
Romelu Lukaku is high on the list of potential replacements after the Belgian scored 25 league goals for Everton last season.
Lukaku joined Chelsea as an 18-year-old in 2011 but was given limited chances in the first team and eventually moved to Merseyside three years later.
"Chelsea bought that player as a youngster and maybe it was too early or whether he didn't get the chances I don't know," Lampard said.
"But I love his attitude, the way he plays and very determined. I remember training with him and he was always practising and he wanted to score goals. I respect lads like that.
"He deserves the best and if Costa does move on and they want to get something like for like in the style of a big front man who score goals then Lukaku has proved he can do that."
Lampard's old team-mate John Terry is also on the look-out for a new club after Chelsea chose not to renew his contract, which expires at the end of the month.
Terry reportedly has offers from a handful of Premier League teams, as well as Birmingham and Aston Villa, while a move to China or America is also an option for the 36-year-old.
"I haven't spoken to him, I'm not in the position to give advice because for me these decisions are completely personal," Lampard said.
"I know when I had my decisions to make late on in my career, they're the toughest ones I had to make because it's easy when you're 25 and you get offered contracts to go places you want to be for five years.
"It changes when you get older. For John it's not just football it's a family matter and it's your body and how you feel about everything.
"All I would say generally is if he still has a desire and feels he's ready to play on, then play on because you are a long time retired."
Lampard left Chelsea in 2014 to join New York City before returning to England for a season on loan at Manchester City.
The former England midfielder said if Terry asked about playing in Major League Soccer, he would give a glowing recommendation.
"If someone like John Terry is thinking of playing there, and any other players, I would only have great things to say about it," Lampard said.
"Go there and play, the way of life over there is brilliant, most stadiums are selling out week in week out. It's growing fast so I would only have positive things to say."
Lampard was speaking at the MLS Heineken Rivalry Week Viewing Party in London.