Welsh boss Mark Hughes (pictured) has taken the precautionary step of naming a larger than normal party, with the possibility of a number of withdrawals taken into account.
Wales - who top Group Nine - will be looking to remain unbeaten as they host Azerbaijan at The Millennium Stadium on March 29 and then travel to Belgrade just four days later.
"We have to cover ourselves as we lose some of them," explained Hughes.
One major problem for the Manchester United legend could be the right back berth, with Mark Delaney already ruled out and Cardiff's Daniel Gabbidon struggling with a back problem.
"The biggest doubt is Gabbidon," Hughes confirmed.
"He has been out for a long while with his problem and I would have hoped that he would have been back by now.
"He certainly won't be involved in any of the build-up and is probably going to miss the games anyway."
Hughes has called up Gabbidon's team-mate Rhys Weston - a central defender - as cover and he could use the former Arsenal stopper or even Leicester's Matthew Jones at number two.
"I will have to play someone there who does not play in that position for his club," confirmed Hughes.
"Weston and Matty Jones can both do the job but we'll have to wait and see until nearer the match."
Squad in full: P Jones (Southampton), Crossley (Middlesbrough), Ward (Nottm For), Coyne (Grimsby), Melville (Fulham), Symons (Crystal Palace), Page (Sheff Utd), A Williams (Reading), Gabbidon (Cardiff), Barnard (Grimsby), Weston (Cardiff), Speed (Newcastle), Pembridge (Everton), Savage (Birmingham), Davies (Tottenham), M Jones (Leicester), Robinson (Portsmouth), Johnson (West Brom), Oster (Sunderland), Trollope (Northampton), Koumas (West Brom), Giggs (Man Utd), Hartson (Celtic), Blake (Wolves), Bellamy (Newcastle), Taylor (Burnley), Earnshaw (Cardiff).
