Martinez told evertontv: "It is going to take a long period of time, which at this stage of the season will be a big miss. It will be weeks rather than months.
"It's a really disappointing outcome. He was ready and had been working really hard since he arrived at the club. Starting the game at Chelsea was the next target after Swansea and for him to pull his hamstring in the last action of the warm-up was a really disappointing moment.
"We are a little bit concerned. We are working with his parent club and making sure we get the right diagnosis. Lacina was really down after and we need to support him. We will find out over the next 48 hours how we will treat the injury."
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