Eidur Gudjohnsen believes his former Iceland team-mate Gylfi Sigurdsson could be tempted to leave Swansea if a big club comes in for him this summer. Sigurdsson's future has been the subject of fierce scrutiny after a season in which he was one of the most effective performers in the Premier League. The 27-year-old scored nine goals and had 13 assists as he helped Swansea avoid dropping out of the top flight.Swansea are determined to hold on to their prize asset, but Everton and Tottenham have both been strongly linked with Sigurdsson. Leicester could also see him as an ideal replacement for Riyad Mahrez, who has reportedly declared his wish to leave the Foxes this summer. "Gylfi has had a really good season," former Barcelona and Chelsea player Gudjohnsen told Press Association Sport."He's obviously been one of the most important players in keeping Swansea in the Premier League."He's got tremendous quality, but he can still improve on certain things whether he stays or go."But he's come to an age where he might want to try his luck at a bigger club or even European football."It's all down to him. If he's happy where he is, he should stay."It was reported last month that Swansea had agreed a Â£25million transfer fee with Everton for Sigurdsson.But Swansea quickly dismissed those reports and Press Association Sport understands that the club value the Icelandic playmaker at Â£40million.Swansea chairman Huw Jenkins revealed in February that Sigurdsson - who signed a new four-year contract 10 months ago - was the subject of "substantial offers" during the last transfer window.And owner Steve Kaplan last month expressed Swansea's desire to keep Sigurdsson, saying: "We all know how important Gylfi is, just as he knows how much he's valued and loved here."There's been interest in him before - there were some pretty big enquiries about him last summer and in the January window - but we didn't want to sell him then and we don't want to sell him now."Sigurdsson has said that he is happy at Swansea and would only leave the Liberty Stadium if the club wanted to sell him."I signed a new contract in the summer and I've got three years left," Sigurdsson said last month. "So it's down to the club if they want to sell me. But I was very happy when I was on loan here and then again in the last three years. "I'm not trying to leave, I'm not desperate to go or anything."