Nemanja Vidic has warned of the pressures international duty can place on players in the Barclays Premier League.
Although concussion sustained in the Reds' victory over Wigan meant Vidic missed Serbia's Euro 2008 qualifiers this week Saturday's 0-0 draw with Armenia and Wednesday's 6-1 win in Azerbaijan the defender said many of his United team-mates will be tired after stints representing their countries.
Most players away on international duty will have boarded flights back to Manchester in the early hours of Thursday morning, but Friday's training session at Carrignton will be the only full run-out they'll have before Saturday's trip to Villa Park.
And Vidic says it's important to remember the effects of long-distance travel on the body. Wayne Rooney and Rio Ferdinand have both returned from Russia, Darren Fletcher from Georgia and Cristiano Ronaldo and Nani from Kazakhstan. Meanwhile, Carlos Tevez has been in South America representing Argentina in World Cup 2010 qualifiers.
"There have been a lot of games for the players and we always find the match after an international break is very tough," Vidic told ManUtd.com.
"It's hard to come back to the club and adapt your game everyone plays differently on international duty. When you return to United you have to find your feet again and it can take a few days to settle."
Vidic also suggested United's non-English players find the going even tougher.
"It's very hard when I have a home international game in Serbia, for example. I get to see my friends and family, which is nice, but that can take it out of you and it means you get less time to yourself to rest.
"Then again, when I'm playing for United I feel very professional because I don't have those distractions. I have a lot of time for myself to rest, think about the next game, prepare for the training sessions. I'm very comfortable here."