Romain Grosjean dominated practice, finishing a second clear of Dani Clos and local boy Stefano Coletti after being one of the drivers least affected by traffic, minor accidents, yellow and red flags through the half hour session.
The start of the practice session was delayed by track staff having to make repairs to the tyre barrier at St Devote after Michael Schumacher's run-off there during the morning F1 practice session.
The GP2 practice finally got underway at 12.10pm, and was then further curtailed by a brief red flag required while marshalls cleared debris from the track following a crash between Charles Pic and Luiz Razia in turn 16 through the swimming pool. Pic had been slowing up to give himself some room on the packed track and Razia simply didn't spot the danger and went into the back of the Barwa Addax.
There were also yellow flags late in the session for separate spins involving Fabio Leimer at Mirabeau and Luca Filippi in Casino Square but both drivers kept their cars off the barriers, while the end of the session was compromised when Davide Valsecchi spun the AirAsia in the final corner and hit the barriers at Anthony Noghes, wrecking his rear wing and leaving debris in the middle of the track.
Full session times and positions
Qualifying for the feature race will be held from 4.15-4.45pm (3.15-3.45pm BST), with the feature race scheduled to start on Friday morning from 11.15am (10.15am BST). Jules Bianchi will have to take a five place drop in his grid position wherever he qualifies this afternoon, after being penalised
for causing a starting grid accident at the Barcelona sprint race last Sunday.
Oliver Turvey replaces Mikhail Aleshin
in Monaco, while Alvaro Parente continues to sit in for Christian Vietrois at Racing Engineering and Kevin Ceccon for the injured Davide Rigon at Coloni.