Queens Park Rangers suffered a 3-1 defeat to Fulham in the Championship on Saturday.
Mortimer made the comment during the closing stages of the Championship game between QPR and Fulham at Loftus Road.
Rangers lost the London derby 3-1, with some fans leaving the stadium before the final whistle.
“You can feel sorry for the QPR fans,” said former Charlton Athletic midfielder Mortimer on BBC Radio London. “They cannot keep possession and the quality is of such a poor standard.”
First-half goals from Ross McCormack, Moussa Dembele and Tom Cairney saw Fulham go 3-0 up, with Tjaronn Chery pulling one back for Jimmy Floyd Hasselbaink’s side in the 91st minute.
Over the course of the 90 minutes at Loftus Road, hosts QPR had 40% of the possession, took 11 shots of which six were on target, and earned six corners.
Visitors Fulham had 60% of the possession, took 16 shots of which nine were on target, and earned five corners.
QPR will return to action next weekend when they take on Bolton Wanderers away from home at the Macron Stadium in the Championship.