Southampton are waiting to learn the extent of the hamstring injury suffered by striker Shane Long against Inter Milan on Thursday.
The Republic of Ireland international pulled up three minutes into the second half of Saints' 1-0 defeat at the San Siro and had to be replaced by Charlie Austin.
Manager Claude Puel has yet to discover how serious the problem is, but he confirmed Long will not be available for Sunday's trip to face Manchester City in the Premier League.
"Shane Long will be out with his hamstring injury," said the Frenchman. "I don't know for how long at the moment, I will have a look but I don't know the timescale of the injury."
A prolonged absence for Long could lead to a run of games for Jay Rodriguez. The former Burnley forward insisted his fitness was not a concern after passing up the chance to give Southampton the lead in Milan.
The 27-year-old was put through on goal after nine minutes, with the score at 0-0, but hesitated before losing possession when well placed to score. He demonstrated a similar lack of confidence later on, and was substituted as Saints fell behind.
Rodriguez is back making regular appearances having suffered anterior cruciate ligament damage in 2014.
"I feel fine, I feel great," Rodriguez said. "I just want more and more of it. That's what I need and I'm sure the goals will come. I just need to keep my fitness and keep on the field.
"I need regular games. That's the main thing. I need a run of games to find my form and the goals will come.
"It's one of those things, it just happens, but I'm working hard to keep extra fit and I'm sure I will be.
"I cut inside and I should have squared it or taken the shot early. It was just one of those things. I should have decided earlier what I was going to do.
"I'm not happy. I'm always like this after a game if I haven't scored. We came here to win and we had the chances to and, although we're disappointed, we can't keep our heads down."
The result meant that Southampton slipped to third in Group K.
It also gave Inter their first points of the competition and left the pool wide open when the Italian side -- who visit St Mary's in a fortnight -- had been at risk of elimination.
Asked about the competitive nature of the group, Rodriguez said: "We know that but we've got home games now and that'll be a strong point for us. We have to focus on the next game.
"It's a proud moment [to play at the San Siro] but it doesn't really mean anything when you lose. We have to now focus on Sunday."