Jayasuriya, 38, retired from international cricket earlier this year but he has now re-considered his decision after impressing in the Indian Premier League Twenty20 competition.
He has now been named in Sri Lanka's squad for the Asia Cup in Pakistan, which clashes with the Twenty20 Cup, and pulled out of his contract with Warwickshire.
"This has come out of the blue and it is a big disappointment for us," said Ashley Giles, Warwickshire's director of cricket.
"Sanath had retired from international cricket to play for us but it now seems that he has enjoyed his cricket so much that he has reconsidered his decision to retire at international level.
"He has told us that he made his decision at the request of the sports minister which probably means the prime minister.
"But it leaves us without an over-seas player for the Twenty20 and with not much time to find a replacement.
"When you look at the teams that are involved in international cricket during the Twenty20 Cup there aren't too many options."
Warwickshire might also have to find a replacement for South African fast bowler Monde Zondeki who limped out of the attack against Middlesex yesterday with a groin strain.
As Zondeki was awarded a central contract by South Africa on Monday and he is likely to be included in their squad for the tour to England in July and August, Warwick-shire expect him to be recalled to South Africa as a precaution.
If Zondeki's first stint in county cricket is cut short Warwickshire are expected to seek two overseas players to cover the rest of the season,a Twenty20 specialist and an experienced seam bowler.