Dwight Gayle suffered an injury after coming off the bench against Southampton.
The Newcastle United striker replaced Joselu in the 68th minute at the St Mary's Stadium this afternoon.
Benitez was hoping to use Gayle pace late in the Premier League game to relieve the pressure on his defence.
But Gayle hurt his calf was struggling for the last 10 minutes of the club's 2-2 draw.
United manager Benitez said: "Dwight, we cannot say too much, because when he came we were expecting to use his pace.
"But he had a little problem with his calf. He was working very hard, but with a problem. In the last 10 minutes we were playing with just 10 players. Even then, he was still running and he was chasing some balls and passing.
"But we couldn't use his pace in the last 10 minutes, and that was a pity because we were under pressure and he was maybe the solution for us.
"But after the run he did, he was feeling a little bit stiff in his calf and he couldn't run in the same way."
Gayle was troubled by a hamstring problem earlier in the season.