The 33-year-old, who made just under 450 appearances for Watford, has been without a club since his release from Vicarage Road in the summer, but featured in the Millers' reserve game with Scunthorpe on Wednesday.
However, boss Neil Warnock said a deal is not likely to be imminent as Doyley is struggling with match fitness.
"He's come up to be with
us for a while. He came to QPR when I was there and he’s a good pro and we’ll
have another look at him," Warnock said.
"I think he’s just
lacking a little bit of match fitness at the minute but we’ll see him this week
in training."
Doyley's arrival in South Yorkshire is a further suggestion that Warnock will turn to experience in his bid to deliver Championship survival after he offered Jerome Thomas a deal until the end of the season.
Thomas, a former Arsenal winger who played under Warnock at Crystal Palace and Leeds, was handed a trial at the Millers by former boss Neil Redfearn, with his successor now opting to take a punt on the 32-year-old.
Thomas, who counts West Brom, Charlton and Portsmouth among his other former clubs said: "The manager and Kevin have
come in and they wanted to get the deal done, I have signed until the end of
the season and we all share the same common objective which is to try and keep
the club in the Championship.
“Initially it looked as
though I was going to the USA or Asia but the opportunity arose to come and
train here and to see if both parties were happy.
“I have kept myself fit, the
training has been very good and Warney has been great with me
helping me do extra.
"I managed to get 90 minutes under my belt in the reserves
last week, and I will be looking to get as many minutes in as possible.”
If Doyley does earn a deal at New York Stadium, he will become the fourth free agent aged over 30 to have been handed a contract this season following in the footsteps of Stephen Kelly, Luciano Becchio and Thomas. Leon Best is 29.
