OM coach Elie Baup said on French television channel Canal+: "He was hit. I hope it's not serious."
Valbuena added: "In my last action, I felt something. I do not want to accelerate. I prefer not to take risks. We'll see after the tests. I hope to return as soon as possible."
Yoann Gouffran scored the only goal of the game seven minutes into the second half as Les Girondins moved up to second - a point above OM - in the standings.
Baup was disappointed to be heading back to Marseille empty-handed.
"This is an opponent who did not look like troubling us," he said on www.om.net.
"The match was very balanced, with both defences strong. Both teams were solid, well organised. We had opportunities with
He added: "We have a game in hand but it is never good to lose points against a direct rival."
Monaco moved back to second in Ligue 1 with a hard-fought 1-0 win over 10-man Ajaccio at the Stade Louis II.