Boonen finished in 65th place, 27 seconds off the pace of stage winner Marcel Kittel (Argos - Shimano), having decided to race the French event over the Tour of California given his lack of race miles. Teammate Andy Fenn was sixth.
"Remember that after my crash in the Ronde that there was nothing I could do for four weeks and only then have I been easing into it," he told HLN.be. "More than anything I am trying to get to the end of the season in the best shape possible. Maybe there will be some nice results for me in September or October."
Boonen escaped his crash at the Tour of Flanders with a rib fracture but also suffered various injuries when he hit a road sign 19km into the race. He fell on his left side, injuring his left knee, elbow and hip while also sustaining a contusion and a wound on his right knee that required stitches.
The three-day Tour of Picardie continues on Saturday with a 171 km stage to Bailleul-sur-Thérain.