Jose Mourinho remains a better manager than Pep Guardiola, according to Middlesbrough boss Aitor Karanka.
Manchester United have endured mixed form under Mourinho this season, with their 2-1 Europa League defeat to Fenerbahce meaning they have managed just two wins from their last seven matches in all competitions.
By contrast, Manchester City sit top of the Premier League - eight points clear of United - and dispatched Barcelona 3-1 in the Champions League on Tuesday to move to within touching distance of the knockout phase.
But Karanka, who was Mourinho's assistant at Real Madrid, says the Portuguese still has the edge over the former Bayern Munich boss.
"For me, yes Jose is better than Pep," Karanka said ahead of Middlesbrough's clash with City on Saturday.
"I have been working with him [Mourinho] for three years and I know his methodology, I know his character, I know everything. For me, it has been amazing to work with him, so I know him better than Pep."
He added of Guardiola: "We are not really friends because Real Madrid versus Barcelona were such big games and I wasn't with him in the national team so I didn't have a relationship with him.
"He is one of the best coaches, but I don't think one is much, much better than the rest because we have Jose, we have Pep, but we also have Diego Simeone in Spain, Jurgen Klopp here, Mauricio Pochettino, Antonio Conte with Chelsea and Massimiliano Allegri in Italy."
Indeed, Karanka believes Arsenal - who were held to a 0-0 draw by Boro last month - are very much a match for City.
"I don't think this is the best team I've faced here at Middlesbrough," he said. "When we played against Arsenal in the cup two years ago, if you look at their team and the players they had on the bench, it was amazing.
"It was 18 amazing players. Maybe not better than Manchester City now, but certainly no worse than the team we will be playing against at the weekend.
"Will this City team win the league? I think it is hard to say. There is Man City, but there is also Arsenal and Chelsea right up there. There are a few teams who will think they can win."
Alvaro Negredo is in line to face his former side at the Etihad Stadium and Karanka expects the striker to be determined to prove a point, after he struggled for form in the latter part of his one season with City.
"I don't know exactly what happened but as a striker you can probably think that it was a lack of confidence," he said. "If you are in a team like Man City and you start losing your position, it can be hard to go back to your best again.
"I think it is an extra motivation for him. When you have played in a big team and now you are facing up against them in their stadium, it can be an extra motivation to do well."