The giant three-quarter limped off during the closing stages as Bath made it two wins from two at the start of the new season, punishing Wasps for a series of costly errors.
Banahan left the Rec in a brace, and Bath skills coach Brad Davis admits it will be a waiting game to determine the severity of the problem.
He said: "Matt has damaged his knee and we will know more about it in the next 48 hours, he will go to have a scan and we will wait and see what the results are, but he has been put in a brace."
Head coach Toby Booth added: "All injuries are a worry. The people who are near the top of the table at the end of the season are the sides whose players stay fit and healthy, giving them more firepower at their disposal.
"We have a few dents in the squad already but we will have Sam Vesty, Stephen Donald and Tom Heathcote to come back soon."
Banahan had earlier run in Bath's first try of the afternoon, handing off a weak tackle from Elliot Daly in his way.
Further scores followed from wings Tom Biggs and Kyle Eastmond, the latter scoring his first try since joining the club from St Helens, with Olly Barkley adding 15 points with the boot.
Two Nicky Robinson penalties had kept Wasps in it at the break and Tom Varndell and Christian Wade crossed in the second half for the visitors.
But as with their surrender of a 27-point lead against Quins last week, it was missed tackles and unforced errors that did for Dai Young's side, who did at least secure a losing bonus point thanks to Robinson's last-gasp penalty.
Eastmond's performance was particularly eye-catching. The former rugby league man had an injury-hit first season in union last term, but his pace and trickery made him a constant menace to Wasps.
And there were plenty of dangerous signs for future opponents in his willingness to come infield and fill in at half-back, where he plied his trade for Saints.
One of his forays off the flank resulted in his try, jinking and twisting through several feeble Wasps tackles to get over.
Davis said: "He is a smart player, we knew that when we signed him. His ability has never been in doubt and the try he scored was a contender for try of the season.
"Apart from that he has a lot about his game in terms of passing, kicking and running. He is one of the best at the club and we are very pleased with his development."
Wasps boss Young was left unimpressed by his side's performance but would not single out individuals for criticism despite missed tackles and a loose pass gifting Bath their tries.
Young said: "We looked dangerous in open play and that was it, we had no patience with the ball and we offloaded when it was not on.
"Whenever the game got loose we looked dangerous but we never looked like constructing anything ourselves and Bath did the basics better than us. They had a good scrum and driving line-out and they did what was needed."
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