Just before Jose Mourinho delivered his curiously upbeat assessment of Chelsea’s performance in the 2-1 defeat at Porto late on Tuesday night, John Terry was out for a solo warm-down on the pitch. The 2,500 Chelsea fans, kept behind in the top tier of the Estadio Dragao, sang “we want our captain back”. Terry waved and applauded in return.

The demotion of Terry to a bit-part player has been one of the strangest parts of what is becoming a difficult season for Chelsea. Gary Cahill and Kurt Zouma have started together in their last four matches at Premier League and Champions League level. Terry’s one recent outing was against Walsall in the Capital One Cup last week in a Chelsea team featuring Kenedy, Ruben Loftus-Cheek and Baba Rahman.

When asked before the game about Terry’s occasional role, and how he dropped Iker Casillas when Real Madrid coach in 2013, Mourinho said the reasons were purely sporting. “Every time a big player is not playing you have to try to find more than just a football reason for it,” the Chelsea manager said. “Many, many times it is just a football reason for it.”

Porto 2 Chelsea 1 player ratings Show all 11 1 /11 Porto 2 Chelsea 1 player ratings Porto 2 Chelsea 1 player ratings Asmir Begovic: 8 out of 10 Was Chelsea’s best player on the pitch. The goalkeeper made several reflex saves to deny the likes of Aboubakar and Brahimi throughout the game and, despite his one-handed stop to keep out Brahimi’s first-half effort, he could do nothing to stop Andre opening the scoring. Porto 2 Chelsea 1 player ratings Branislav Ivanovic: 4 out of 10 After failing to clear an early Porto effort, the full-back – acting as captain in John Terry’s absence – allowed Brahimi to dribble past him all too easily seconds before the opener. Although he made a vital block to deny the Porto midfielder in the second half, Ivanovic should have equalised but headed Willian’s corner wide. Another under-par performance from the right-back. Getty Images Porto 2 Chelsea 1 player ratings Gary Cahill: 4 out of 10 Failed to shepherd his back line well enough during the set piece that Maicon made it 2-1 from, and should have done better to mark the Porto defender at the same time. Was often dragged out of position and didn’t show the leadership skills that were sorely needed to control the likes of Aboubakar. Getty Images Porto 2 Chelsea 1 player ratings Kurt Zouma: 5 out of 10 Failed to put in the strong and dominating displays he has shown in the past and looked uncomfortable as he and Cahill were too often run past by Aboubakar and Brahimi. Communication between the pair is appearing to be an issue. Getty Images Porto 2 Chelsea 1 player ratings Cesar Azpilicueta: 6 out of 10 Defended well early on and literally put his body on the line to keep out an early shot, but did not see Andre advancing for the opener. Was then shown a yellow card for pulling the Porto winger back and began to lose the battle to control him in the second half. Getty Images Porto 2 Chelsea 1 player ratings John Obi Mikel: 5 out of 10 Looked good in the early stages of the game, but failed to really control Brahimi in the middle of the park, which led to the Porto man running riot and being involved in the opening goal. Was replaced by Hazard in the second half. Getty Images Porto 2 Chelsea 1 player ratings Cesc Fabregas: 4 out of 10 Tested Casillas with a long-range shot in the sixth minute that proved to be one of Chelsea’s best chances early on, but the Spaniard failed to once again impress when needed to create attacks. 2015 Getty Images Porto 2 Chelsea 1 player ratings Ramires: 6 out of 10 Was deployed on the right and his inclusion in the starting XI paid off when the Brazilian won the free-kick that Willian scored from. However, he was later out-muscled by Maicon, which allowed the Porto captain to seal the win. Was taken off in the 70th minute for Hazard. Getty Images Porto 2 Chelsea 1 player ratings Willian: 8 out of 10 Worked hard in midfield and, on more than one occasion, the Brazilian tracked back to help defend. He capped off a good display with a brilliant free-kick that restored parity for the visitors. Getty Images Porto 2 Chelsea 1 player ratings Pedro: 4 out of 10 Mourinho started the Spain international on the left after utilising him on the right following his summer move to the club and, aside from his powerful shot that Casillas saved in the 13th minute, Pedro disappointed. He failed to provide the service that Costa desperately needed and was taken off in the second half. Getty Images Porto 2 Chelsea 1 player ratings Diego Costa: 6 out of 10 Despite missing Chelsea’s last two games, the striker was lively and got past Maxi Pereira time and time again in the first period. He was unlucky not to have scored when his powerful curling shot hit the bar in the second half, but the main issue for Costa was that he was left isolated too often – which forced him to drop deep to find the ball. Should have been awarded a penalty when his shot ricocheted off Marcano’s arm in the area with minutes of the game left. Getty Images

But it is difficult to avoid the feeling that the relationship between Terry and Mourinho has cooled. The footballing case for his continued exclusion is not obvious. Mourinho praised his side’s “good performance”, albeit with “two ridiculous mistakes”, on Tuesday night, but they could easily have conceded three or four goals.

Chelsea have conceded goals from corners in their last two matches, in the 2-2 draw at Newcastle on Saturday and against Porto. That is why they need Terry back in the side.

Jason Cundy, the former Chelsea defender and close friend of Terry, suggested there was a personal or political element to recent events. “If you’re going to drop him, that’s fine, it happens in football, but I think Mourinho is sending out a message,” he said on TalkSport. “John Terry hasn’t played badly this season and I think he’s been really unfairly treated. I don’t think he’s played badly enough for him to be on the bench.”

Branislav Ivanovic, in contrast, is certainly playing badly enough to be on the bench and yet he continues to feature. He managed to survive Mourinho’s cull on Tuesday, appearing again at right-back, where he was given yet another very uncomfortable outing, this time by Yacine Brahimi. Ivanovic is in the last year of his Chelsea contract, and while he has been offered one extra year, his drop in form during the uncertainty has been noted. He is unlikely to still be at Stamford Bridge next season.

There would be a strong case for dropping Ivanovic and Zouma against Southampton on Saturday and bringing back Terry and Rahman, thereby allowing Cesar Azpilicueta to move across to right-back. But Terry struggled against the pace of Southampton striker Sadio Mané last season, and given Mourinho’s desire to defend slightly higher up the pitch this season, he could well stay on the bench, despite what the fans think.

Diego Costa was one of the few Chelsea players to speak publicly after Tuesday’s game, admitting that Chelsea have “lost some confidence” after their recent poor run of results. “‘We are all united,” Costa said. “It’s not a good moment now. We must do more. We have a good squad with a great deal of quality. We have maybe lost some confidence in three or four games.” There was also a tacit admission from Costa that Mourinho was right about the players’ attitude, which he criticised so bluntly on Monday.

“The manager knows the quality of his team,” Costa said. “He knows what we can do. It is the responsibility of all of us. We have to improve our character and confidence.”