Jonas Gutierrez claims he was told by Newcastle's club doctor not to worry about pain and discomfort in his groin which he experienced during the 2013 off-season.
The midfielder told a three-strong panel of his employment tribunal he raised the issue of pain during sex, or when wearing tight underwear, after reporting back for pre-season training in July 2013.
Gutierrez, currently playing for Spanish side Deportivo La Coruna, spent seven seasons with Newcastle after joining the club in 2008, and underwent an operation to remove a tumour in his left testicle in October 2013.
Gutierrez said in his witness statement: "I discussed my concerns about my groin with Paul Catterson, the club doctor, on three or four separate occasions as the discomfort and pain had not subsided.
"On each occasion, he simply told me not to worry and dismissed these symptoms as nothing serious."
Further alleging that he was then forced to play in 2013-14's opening fixture at Manchester City because a team-mate refused to play, Gutierrez asserted: "On the team bus I was surprised to be told by my manager that I was to play in this match.
"This was because my Newcastle team-mate Yohan Cabaye had refused to play as he had requested a transfer from Newcastle to Arsenal.
"Therefore despite not being fully fit and against doctor's orders, I was selected to play from the start in the match against Manchester City."
Gutierrez was substituted just before half-time, having aggravated a pre-existing thigh injury, the tribunal was told.
The player then failed to feature due to injury until making an appearance from the bench against Cardiff City on October 5, 2013.
Gutierrez told the hearing: "Whilst I was injured I continued to raise my concerns with Paul Catterson about the discomfort and pain in my groin.
"Around the end of September I noticed that my left testicle had become inflamed and I spoke again to Dr Catterson about this in early October.
"It was only at this stage that he seemed to take my concerns seriously and booked me in for a scan.
"Eventually on October 14, 2013, I underwent an ultrasound scan which detected a tumour.
"I was very upset when I was told about the tumour, particularly as I had raised my concerns about this for so long."
The tribunal continues.