Antonio Conte admitted on Wednesday that the departure of Matic was a "great loss" to Chelsea, who will also begin their Premier League title defence without £40 million signing Bakayoko due to a knee injury picked up in the final weeks of last season at Monaco.

Lampard has no doubt that Matic's arrival will make United stronger.

"I was surprised because selling to a direct rival isn't the norm at the top end," the BT Sport pundit said in an exclusive interview with ESPN FC.

"It was a big deal when Chelsea sold Petr Cech to Arsenal. People at the club seemed to mull it over for quite a while and then out of respect for Petr and what he'd done, and the situation with [Thibaut] Courtois, they let him go.

"This doesn't seem quite the same, but at the same time we don't know whether Matic wanted to leave. Was it his dream to go and play for Manchester United? Did he want a new challenge at 29?

"There are a lot of variables that aren't easy but from the outside, it does seem strange to let that player go to a direct rival -- and he will improve them. It was certainly a position that Manchester United as a team needed to strengthen, and they've gone and done it with Matic."

Matic's departure will force Conte to accelerate Bakayoko's progress into the starting XI when he returns to fitness. Lampard does not believe the situation will make the Frenchman's adaptation to the Premier League harder, but he conceded that the challenge facing the 22-year-old is a significant one.

"There's pressure, but coming for £40 million from Monaco after a great season, the pressure was going to be there regardless," Lampard added.

"Matic was very important and sometimes you could look past him at other players like [N'Golo] Kante, Hazard, who catch the eye, but he played a very positionally disciplined role for Chelsea with the way they go forward.

"There's responsibility on Bakayoko not just to bring the talents that he has -- and he has many -- but also the discipline to fit into the system."

No new Chelsea signing is under more pressure than Alvaro Morata, brought in for a club-record initial fee of £58m from Real Madrid to replace the unsettled Diego Costa as the focal point of Conte's attack.

But Lampard believes the 24-year-old's determination to force his way out of a comfortable situation in the Spanish capital is a good sign.

"Being the main striker for a club like Chelsea, like Manchester United, like Real Madrid, like Barcelona, brings a lot to it," Lampard said.

"That's the pressure he probably hasn't had. I know he was at Juventus but I don't think he was ever completely their No. 1 striker, slightly in and out at different times. At Real Madrid, certainly, he was in and out, so the main pressure for Morata is to say, 'Here I am, I'm the No. 1 striker and I can take this all on.'

"I think he's got all the tools to do that. He's got great movement and he's a good finisher, so he now needs to adapt to the Premier League. He won't have had anything like it in Italy or Spain. We are the most physical league. It's a very tough league and he'll have to stand up to that.

"I do think he's got the natural talent to come in and score the 20-plus goals that Diego Costa scored last year."

Costa's rollercoaster Chelsea career is ending in acrimonious fashion, but Lampard thinks now is the right time for player and club to part ways.

"He seemed like he wanted to leave last year at times, although he was very influential and played very well," he said of Costa. "It's gone beyond now and it's time [for him] to go.

"I don't think the club wanted to let Diego Costa go necessarily, because you can't get Diego Costas on every street corner. He's a very select player who's a top, top striker, but when the position goes so far it's difficult to put it back. I think we just have to accept it and move on."

Conte has repeatedly stated Chelsea's need to improve their squad depth in the final weeks of the summer transfer window, and Lampard remains confident that the Premier League champions will get the players they need to compete on four fronts this season.

"I think they've bought well -- it's just a case of numbers," he insisted. "They've had an outflux, a lot of players have gone but most of them were squad players and young players who probably won't affect the first XI that much.

"But I understand people's fears. As a Chelsea fan you're always going to want more: 'Can we buy the best players? He's available, can we get him?' I think Chelsea more often than not have backed their managers and brought in the players needed.

"They've been very successful over the past 10 to 15 years, so I think you have to have faith in that. You have to have faith in the manager. Hopefully by the time the window shuts it all comes together, and then the club moves forward."