Van der Sar was left out of the team for Manchester United's 4-2 win over West Ham on Saturday as a precaution after sustaining a groin problem, and Tomasz Kuszczak - who took his place at Upton Park - was sent to warm up on two occasions at Stamford Bridge.
However, Van der Sar - who was booked for time-wasting when Vidic went to take a goal kick - has suggested the problem was caused by cramp.
"When I dived to save a shot from Torres, I went 105% for my take-off," he said. "My calf gave way a little bit and I ended up with cramp.
"I didn't train a lot in the last couple of weeks, so maybe it was a bit of tiredness or something."
Manchester United play Fulham in the Premier League on Saturday before hosting Chelsea for the second leg of their Champions League tie on Tuesday.