Rafael Benitez has conceded Chelsea will not be at full strength when they face Manchester United in an FA Cup quarter-final replay on Monday as he prepares to name a strong line-up against Southampton on Saturday.
Chelsea face the Saints in the Premier League just two days before they host United, with both games significant to their season and Benitez's future at Stamford Bridge.
Although Sir Alex Ferguson is likely to rest a number of key players for United's trip to Sunderland, Benitez admits he cannot afford that luxury as the Blues close in on second-placed Manchester City.
"We can't do that. The difference between them and us is that they are 15 points ahead (at the top of the Barclays Premier League)," Benitez said.
"It is not an excuse. The reality is that their position in the table gives them an advantage and they are out of the Champions League. Their priority will be the FA Cup.
"We have to pick a very competitive team for Southampton. If we can beat Southampton we will be keeping an eye on (trying to catch) Manchester City."
A chaotic fixture list over the next fortnight could prove decisive for Chelsea with quarter-final clashes in the FA Cup and Europa League.
Captain John Terry, Gary Cahill and Ramires are all expected to be fully fit for Monday's match, although Cahill and Ramires could be sidelined for the trip to St Mary's.
Benitez is likely to rotate his strikers for the two matches, but the Spaniard is concerned about the fitness of his players.
"It is not easy to make a decision (on selection) because it is impossible to be fully fit for the second game," he said. "The day after a game you feel tired, two days after you feel even more tired. That is the reality. The second day will be really tough for everyone.
"All of them they can play (two games in 48 hours) but at what level? Sometimes you can do it if you are not 100% but it depends on each position and each player."
Information from the Press Association was used in this report.