Chelsea boss Maurizio Sarri believes that Manchester United are starting to pay for their decent run of form with their recent displays.
United were spurred on after the sacking of Jose Mourinho and when Ole Gunnar Solskjaer took over as temporary boss they hit some superb form.
The Norwegian got the full-time position but the Red Devils have now lost seven of their last nine matches in all competitions, including an exit from the Champions League and a 4-0 humiliation by Everton.
However, Sarri has put it down to the energy expended by United during that run and also the European competition.
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"They did very well for three months and, probably, in the last period, they paid something," Sarri said. "I think that can happen. But I think that, for us, Sunday will be really a very difficult match. They lost the derby, so their level of motivation will, for sure, be very high.
"[It is difficult for] All the teams involved in European competition. After 55 or 56 matches, playing every three days, it's very difficult. Difficult for us, but difficult all the teams involved in European competitions.
"It's a problem. It's not easy for an English team to solve this problem. It's very difficult to arrive at the final part of the season with the top physical condition.
"England, you have to play more. Probably Spanish or Italian teams, in this moment of the season, will have played 48/49/50 matches. Here in England, we will play match No57. To have 7-10 matches in difference at this stage of the season is a big difference."
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