He was not offered a new deal at the end of last season after suffering a cruciate knee ligament injury in April and is likely to be ruled out of action until Christmas.
Speaking to coveted fan channel Arsenal Fan TV, Lampard felt confident that his former side could retain the title this season, despite losing star striker Diego Costa.
He has trained with the club during his rehabilitation, though, and Mourinho has made clear he still believes the forward can do a job for him.
He said: "I think the champions are the team to beat - they weren't champions for nothing". But also the motivation is higher.
Dressed rather like an American college student in beige trousers, a black top and white pumps, he cut a relaxed figure on the touchline, knowing, perhaps, that there would be tougher tests ahead.
"You know, he's injured, he needs time to recover", the United boss said. The training routines are much better organised.
But City, boosted by a £200million summer spending spree, were ruthless in overcoming the stubborn Seagulls, with Sergio Aguero's goal after 70 minutes followed by Lewis Dunk's own goal.
The former Sweden striker was United's top scorer last season, hitting 28 goals as they won the Europa League, the League Cup and the Community Shield.
Sofiane Feghouli, Cheikhou Kouyate, Diafra Sakho, Andy Carroll, Manuel Lanzini and Michail Antonio are all out of the trip to Manchester United.
European football is now such a big business it's only inevitable that titles are decide by the matter of which Russian oligarch or Arab oil baron invests his money more wisely, and the vast majority of clubs in Europe's top flights are heading into the new campaign with the depressing knowledge that they have no chance of even coming close to the title. Busquets has struggled since they shunned tiki-taka as their style of football, if Valverde does not plan to bring back tiki-taka to Camp Nou, he can afford to lose the Spaniard and instead replace him with a destroyer, one which will help the present Barcelona team and style.
Sky's on-demand service is currently offering its monthly Sports Pass at a considerable discount, that gets you 40% off the monthly fee.
He achieved the feat at Porto, Chelsea twice, Inter Milan and Real Madrid, with the only exceptions to the rule being his first two management roles, at Benfica and Uniao de Leiria, where he lasted less than a season in both cases. This year the Hammers have another problem as their London Stadium is hosting the current World Athletics championships.
Mourinho has other good news as the Daily Telegraph says United has received encouragement from Paris Saint-Germain over the potential purchase of Serge Aurier.