The Spaniard was benched for five games earlier this year after a number of poor performances.
Former Blues defender Sinclair told GentingBet: "I don't know the relationship between Kepa and Lampard behind the scenes but it is clear that there is some level of unsettlement, if such a high-profile and expensive goalkeeper is being left out of the side. You need to take into consideration that he is very young and if Chelsea do look to cash in on him and sign another keeper, they won't get back the money they forked out initially.
"I do think that he is a good enough keeper and you can see that when he came back into the team, he started to show the form that he came to the club with initially. So, perhaps he just needed the 'kick up the bum' to push on again because he is certainly a talented goalkeeper, who has everything in his game.
"There is no particular part of his game that I think he struggles with in particular – he's good with his feet, his positional sense and commanding his area is strong and he's a great shot stopper. It's just about his relationship with Frank and how he can continue to adapt after coming over from Spain."
"Nick Pope is an excellent, young English goalkeeper – he's a really professional goalkeeper that is only going to get better. However, I don't think that Burnley will want to sell him anyway. They won't want to be known as a club where anyone can just come in and take their international players. It will be a tricky situation for Chelsea to sign Nick Pope from Burnley anyway.
"Personally, I'd like Kepa to be given another season to prove himself and settle in the Premier League. When you look at other foreign keepers, sometimes it takes them up to 18 months to settle in the Premier League before you start to get the best out of them – you only have to look at David De Gea at Man United. If Kepa does settle, I don't think there are going to be many better goalkeepers than him in the Premier League anyway."