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Pedro picked an injury during warmup before Chelsea’s 3-2 win over Norwich on Saturday and was replaced by Ross Barkley.
N’Golo Kante also missed the victory over Norwich after suffering an ankle injury.
Chelsea boss Frank Lampard gave an update on both players.
“Pedro picked up a hamstring injury and we will assess the severity of it over the next couple of days, but I think it will be tough for him to be back for next week at first glance,” said Lampard.
“We obviously then have the international break, so that might help, but we will be trying to get him back as quickly as possible because he’s an important player.
“It’s a difficult one with N’Golo because he’s had four years of constant playing.
“We knew he had that injury from the Europa League final last season, which affected his pre-season, and then he picked up an ankle injury last week. He’s trying and we are trying to get him through it, but the game yesterday just came too quickly and he was in too much pain.
“But again he is one to assess and we want him back in the team because he’s an important player. I think the international break will be great for him, to try and recover him.”