The Blues boss admits he has been aware of the defensive issue since before the season began, and he has done his best to counteract it
Frank Lampard believes his Chelsea players are simply not dominant enough in the air to defend or attack well at set-pieces, and they may have to address the issue in the transfer market.
Chelsea suffered a 3-2 defeat to local rivals West Ham at the London Stadium on Wednesday when Tomas Soucek twice had the ball in the net from set-pieces, with the first controversially ruled out by VAR.
The Blues have conceded the highest proportion of goals from corners in the Premier League this season, and although they have a higher average height than six other teams in the league, they appear to be the worst equipped to deal with set-pieces.
Having signed both RB Leipzig's Timo Werner and Ajax's Hakim Ziyech, Lampard's side are in the market for defenders, with Leicester City's Ben Chilwell as a primary target.
They could also sign a central defender, having recently shown an interest in West Ham's Declan Rice - who can also play in midfield - and Bournemouth's Nathan Ake.
Chelsea have long been targeted for their inability to defend set-pieces and Lampard confirms that he thinks the issue is with the players themselves.
"We spoke after the game," Lampard told reporters. "We’ve looked at set-pieces this season. When we came into the club, we looked at the stats from last season. Last season, we were bottom of the league defending set-plays, in terms of teams getting big chances against us, and second bottom in attacking.
"So we looked at that. It’s not just a reference to last season because we haven’t improved much this year.
"If you look at personnel, and I really don’t like to talk about my own playing days, but we didn’t work much at all on set-pieces, certain managers more than others, and there were a few reasons, mainly John Terry, Gary Cahill, Didier Drogba, Michael Ballack and Branislav Ivanovic.
"So you’d stick it in an area and they would defend it or score goals. Similarly with Liverpool, I remember a lot of talk about them and set-pieces a few seasons ago. They were zonal and conceding a lot. They signed Virgil van Dijk and he heads out everything that comes in the box.
"So there’s a huge relation to personnel. If you don’t have that size across the team, the main thing is trying to compete as hard as you can and making it difficult for other teams to score. There’s no doubt and I’m not making excuses because we haven’t done that well enough on the pitch and that has to improve.
"When you look at who you might bring in with the balance of the squad, in the modern day, it is certainly something to take into account when you’re looking at recruitment. Defensively, the players that are here now I have to focus on.
"What happens in the summer will be what happens. I don’t want to talk too far ahead. It’s not the right thing to do. We’ve got a strong group and we’ve got a job to do. We will sit down and look at it in the summer."
Arguably, goalkeeper Kepa Arrizabalaga is part of his side's weakness at set-plays and he faced some criticism for his inability to stop the two crosses reaching the far post to Soucek.
Lampard didn't want to highlight the performances of Kepa amid speculation that both he and the club are looking to move on their £72 million ($92m) signing from Athletic Club.
"I’m not going to talk about any potential, what we may do at the end of the season or not," he continued. "I’m going to focus on what we have got in front of us. With Kepa, there’s been a lot spoken about him this season.
"All I want from him, as I want from all the players, is the right mentality and attitude in approaching the games. I’m absolutely certain I’m going to get that from all of them because I can feel the group at the minute, and they are in that position and he will try and do his job as well as he can do.
"I’m happy with him and that’s how we keep working. That’s the end. I’m not going to keep talking about what may be at the end of the season."
Chelsea now prepare for a match at Stamford Bridge against relegation candidates Watford on Saturday night. The game will mark Lampard's one-year anniversary since it was announced that he would return to manage the club where he enjoyed huge success as a player.
Lampard spoke of how both he and his side have developed during his year in charge as they continue to compete for a spot in the Champions League next season.
He said: "We’ve progressed in the way I want us to play and the style we want to play. When you’re a manager and you come in you have to work very hard at that and there have been some real signs in games where I’ve been really happy with what I’ve seen. In others, not so much.
"I think the expectation at the start of the season, I think even from myself, knowing we lost Eden [Hazard] and the input he had individually at the club was huge, and how do we work around that? I think we’ve found good ways to work around that, I think the development of the youth, the performances of some of the senior players, the way we’re trying to play, I do feel that.
"When I sense from the fans what they want, I always want to improve and we’re nowhere near the finished article where we want to be, but we have found really good levels at times.
"I also understand the second part where you say you will be next, ‘Ok, now we’re going to challenge’, because we’re going up against, if not the two best club teams in the world, then they’re very close to that.
"They’ve worked hard over a big period, they’ve trained well and recruited well, so we may find the curve looks slightly different. We have to fight against that and try and close the gap as quickly as we can in whatever way we can as a club.
"My job on the training pitch is to work to close that gap as quickly as I can. That’s where we’re at. I’m pretty pleased, I’m always a perfectionist and I always want more. I’m pretty pleased but it means nothing if we don’t finish off the season well.
"These next games until the end of the season are huge for us to try and say we’re pleased at the end of the season, because if we get in the Champions League spots then, of course, I will be very, very pleased."