West Brom's 18-year-old striker Stefan Morrison has joined Swansea on a free transfer.
"From what we have seen of Stefan he has impressed us," Martinez told Swans' official website. "He played in a few reserve games for us last season and has been training with us ever since we got back, where he has been impressive.
"Stefan has a great attitude but with every young footballer, he is going to need time to develop.
"But I think he has the chance of becoming a very good footballer."