Ainsworth was Hereford's hero in their midweek FA Cup win at Leeds

The move for the 20-year-old was completed before Thursday's Football League deadline for loan signings.

In return, Watford youngsters Theo Robinson and Toumani Diagouraga, who are currently on loan at Edgar Street, will stay until the end of the season.

Hereford also have the option to make Diagouraga's stay permanent.

606: DEBATE As long as he has a manager who is prepared to give him a decent run in the side, he will shine Number1BrianRice

A Bulls statement read: "Hereford United had no desire to sell Lionel and under normal circumstances would have refused Watford's request.

"However, it was felt that securing the services of Theo and Toumani until the end of the season was vital to us, in our quest to gain promotion.

"It also enhances Hereford's reputation of giving young players an opportunity to develop at our club, important when attempting to sign players either on loan or permanently."

Ainsworth joined the Bulls after being released by Derby in the summer, and has scored eight goals in 19 first-team appearances for Hereford.

He scored the goal that knocked Leeds out of the FA Cup earlier this week, while also netting hat-tricks against Yeovil and Stockport this season.