The Sale Sharks star limped off during his team's dramatic 17-16 Heineken Cup defeat to the Ospreys in Swansea.
And Cueto is now set to undergo an ankle scan as England's Twickenham appointment with the All Blacks draws closer.
"It looked nasty on the television," said Sharks rugby director Philippe Saint-Andre, recalling Cueto's 12th minute exit.
"He will have a scan on Saturday, but Mark is very positive and he thinks it is not too bad."
Robinson and Saint-Andre will hope that Cueto's optimism is not misplaced after he was hurt following a collision with Ospreys full-back Lee Byrne.
Even without Cueto, though, Sale should have grounded the Ospreys, but the hard work and dominance of their juggernaut pack did not get its reward as substitute James Hook converted Wales star Shane Williams' 87th-minute try with the final kick of a disappointing Pool Three clash.
Saint-Andre added: "We were in control of the game, but we were not clinical enough and did not score enough points."
Number eight Juan Martin Fernandez-Lobbe scored Sale's solitary try, while fly-half Charlie Hodgson booted 11 points, yet Hodgson also missed two first-half penalties that were well within his range.
Ospreys head coach Lyn Jones said: "I think there is a 25% improvement to come from us - we need a more accurate kicking game and we didn't play with the width we would have liked. We didn't put our name on the game, if you like."