The 27-year-old joined Boro on a two-year deal from QPR last summer and made 34 appearances in the Championship, however he ended the season second fiddle to Luke Daniels following Chris Wilder’s arrival.
Lumley’s exit is Boro’s third departure of the summer, with Nathan Wood linking up with Swansea City and Toyosi Olusanya making the move north to St. Mirren.
Here are today’s rumours...
1. Watford could sell play-off winner this summer
Watford are reportedly prepared to sell Philip Zinckernagel this summer, with Nottingham Forest targeting their former loanee. Olympiacos are also interested in the 27-year-old. (Nottingham Forest News) | Getty Images
2. Crystal Palace agree deal for West Brom star
West Brom goalkeeper Sam Johnstone is set to join Crystal Palace on a four-year deal this summer. The England international had previously been linked with Tottenham, however they recently signed Fraser Forster. (The Sun) | Getty Images
3. Swansea City boss reunites with defender
Swansea City have snapped up MK Dons' Harry Darling. Russell Martin signed the defender for his former club from Cambridge United last year. (Yorkshire Live) | Getty Images
4. Celtic target Blackburn Rovers youngster
Celtic are keen on signing Blackburn Rovers' Tyrhys Dolan this summer. The 20-year-old made 36 appearances last season and played all over the pitch for the Championship club. (TalkSPORT) | Getty Images