Newcastle United's season took another turn for the worse at the St Mary's Stadium this afternoon.
Benitez's second-bottom side were beaten 3-1 in the Premier League by Southampton.
Taylor and Janmaat – who made mistakes for the first-half goals scored by Shane Long and Graziano Pelle – were forced off.
Janmaat limped off after slipping in the build-up to Pelle's goal, while Taylor was replaced by Jamaal Lascelles at the break, having suffered an injury during the an abject first 45 minutes.
Asked about their injuries, Newcastle manager Benitez said: "I don't know. We will see.
"We have had a lot of them (injuries). We have to see how they are, and after start counting players for the next one."
Taylor mistimed a challenge on Long for Southampton's first goal, scored in the fourth minute.
Asked about Taylor, Benitez said: “He was a little stiff.
"So I think it was a big risk to keep a player with problems on the pitch, especially with the problems we have in defence, so that is why we took Steven off.”
Benitez has a week to assess his squad before United take on Swansea City at St James's Park on April 16.
Fit-again defender Paul Dummett was on the bench at the St Mary's Stadium, while captain Fabricio Coloccini, sidelined since February, is close to a return.