Danny Gabbidon says Ashley Williams would be hard for Swansea to replace.
Swans and Wales captain Williams, 31, has been linked with Everton while West Ham are said to be interested in striker Andre Ayew.
A spokesman said Swansea had not received a formal approach, but boss Francesco Guidolin said he was uncertain about the defender’s future
“Williams is a worrying one, he would be hard to replace,” said Gabbidon, who played alongside Williams for Wales.
“He’s about to turn 32 – time is running out for him a little bit and he probably deserves to play at a higher level and test himself against the best in Europe.”
Williams is due to return to training this week after taking an extended break following Euro 2016, when he captained Wales to their first semi-final in a major tournament.
He has made over 300 appearances since joining the Swans from Stockport County in 2008 and was heavily linked with Everton during the summer of 2015.
At that time the Toffees lined-up Williams as a possible replacement for England international John Stones who was a target for Chelsea and Manchester City – though stayed at Goodison Park.
With Stones again being linked with a move to the Etihad Stadium, new Everton manager Ronald Koemann could need a new central defender.
Ayew was Swansea’s top scorer last season with 12 goals in 35 Premier League appearances.
The Liberty Stadium club have already seen three forwards depart this summer with Portuguese striker Eder joining Lille, Italian Alberto Paloschi going to Atalanta and Frenchman Bafetimbi Gomis signing for Marseille on loan.
The club have been linked with moves for Leicester City striker Leonardo Ulloa as well as Sevilla’s Fernando Llorente.
Swansea begin their top-flight campaign against Burnley at Turf Moor on Saturday, 13 August.