The Premier League leaders visit the reigning Ligue 1 champions in the first leg in Paris on Tuesday for what represents PSG's sixth game in 18 days.
For Chelsea, it is only a fourth in that time period, but Mourinho pointed to PSG's mid-season break as a mitigating factor.
"When the French players were on holiday we played five games in 10 days so don't speak to me about game accumulation," he said in a media conference on Monday.
Mourinho also confirmed that top scorer Diego Costa will return to Chelsea's starting line-up, after missing the last three domestic games for a stamp on Liverpool's Emre Can.
"Yes, I start him," he said. "I don't think it's good for a player to be three weeks or three matches without starting a game."
The Portuguese refused to be drawn on whether Thibaut Courtois or Petr Cech will start in goal and is unsure about Real Madrid and Bayern Munich being given the tag of favourites to win the tournament.
"No. I don't agree, at all. I don't agree because the Champions League is a space for surprises," he said.
Chelsea faced PSG in the quarter-finals last year, when a late Demba Ba strike saw them through on away goals following a 3-1 defeat in Paris and a 2-0 victory in the return leg.
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