Nottinghamshire head coach Peter Moores says he is anxious about the availability of Australia's Peter Siddle because of his back injury.
The 32-year-old first played for Notts in 2014 but missed all of last season - the first of a two-year deal - with a stress fracture in his back.
Moores told BBC Radio Nottingham: "We realise there is real concern over his injury, but we have done due diligence.
"We have kept in touch with Pete and have monitored other overseas players."
Siddle, who has taken 211 wickets in 62 Test matches for Australia, missed the whole of the 2016 domestic season in England, but did return to action for Victoria in October last year.
He took 1-36 and 2-62 in Australia's first-Test defeat by South Africa in November before pulling out of the second Test with his back problem, and has not played since.
"Peter has had a frustrating time," added Moores. "I wasn't here the last time he came, but his reputation amongst the lads is very strong.
"The key is whether he is fit to do what he needs to do. Your overseas players are the key men.
"It is getting close to the point where we have to make a decision, but we feel in a pretty strong situation that if we need to move fast, we can."