England back-row Simmonds, 23, hurt his knee in last week's win over Worcester.

Simmonds has already scored five tries this season and was the Premiership's joint-second highest try scorer last term with 12.

Second-row Hill, 24, who was called up for England's tour to South Africa but has yet to win a cap for his country, has a hand ligament injury.

Both players are being assessed but will certainly miss the Premiership trip to Bath on Friday as well as Exeter's opening two European Champions Cup fixtures.

"It's a little bit early to say how bad they are at the moment," director of rugby Rob Baxter told BBC Sport.

"Hopefully [they will be] back before the end of the season, but I can't really say at this stage."

Baxter added: "You've just got to deal with these things, they happen, and use it to get the guys fit in every other area.

"Both Sam and Jonny can develop other areas of their physique and elements they want to keep working on in their programmes anyway, so we've just got to get them back fit as soon as we can and move on.

"They're both good players and both have a significant part to play in the rest of the season. It's a long old season and it'll be amazing how quick they'll be back in the Exeter shirt."

Exeter have won all five of their opening Premiership fixtures and sit in second place in the table, one point behind leaders Saracens.