$list = [
    '3928.3939392',     //  Should not be matched
    '4.239,99',
    '39',
    '3929',
    '2993.39',
    '393993.999'
];

foreach($list as $str){
    preg_match('/^(?<![d.,])-?d{1,3}(?:[,. ]?d{3})*(?:[^.,%]|[.,]d{1,2})-?(?![d.,%]|(?: %))$/', $str, $matches);
    print_r($matches);
}

Array
(
    [0] => 3928.3939392
)
Array
(
    [0] => 4.239,99
)
Array
(
    [0] => 39
)
Array
(
    [0] => 3929
)
Array
(
    [0] => 2993.39
)
Array
(
)